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Repetitive Project Scheduling:
Theory and Methods
Li-hui Zhang, Ph.D.
Professor, School of Economics and Management,
North China Electric Power University,
Beijing, China
Xin Zou, Ph.D.
School of Economics and Management,
Beijing, China
Translator
Li Zhang
Professor, School of Foreign Languages,
Beijing, China
AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD
PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

Elsevier
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CHAPTER 1
1
Basic Concept
1.1 PROJECTS
Projects can be defined as temporary rather than permanent social sys-
tems, or work systems that are constituted by teams within or across
organizations to accomplish particular tasks. “Temporary” means that
every project has a definite origin and destination, and “particular”
means that the final result of a project cannot be duplicated.
For example, famous projects around the world have included:
• Manhattan Project: developing the first nuclear weapon
• Polaris project: developing a control system for intercontinental
missiles
Ubiquitous projects in daily life include:
• Students’ homework
• Fashion shows
• Highway construction
• Demonstration
The life cycle of a project may consist of four phases: initiation,
planning, execution (including monitoring and controlling), and
close-out. A project places emphasis on process, which is a dynamic
concept. For example, the construction of a highway could be regarded
as a project, but the highway itself cannot be a project.
1.2 REPETITIVE CONSTRUCTION PROJECTS
Repetitive construction projects consist of a set of activities that are
repeated in each unit for the length of the job. After an activity is
started and/or completed in one unit, it must be repeated in another
unit. According to the direction of successive work along the units,
Repetitive Project Scheduling: Theory and Methods.
© 2015 China Electric Power Press. Published by Elsevier Inc. All rights reserved.

repetitive construction projects can be divided into two main kinds
(Vanhoucke, 2004):
• Horizontal repetitive projects are repetitive due to their geometrical
layout; among these, highways, tunnels, and pipelines are classical
examples. These construction projects are often referred to as contin-
uous repetitive projects or linear projects due to the linear nature of
the geometrical layout and work accomplishment.
• Vertical repetitive projects. Rather than a series of activities follow-
ing each other linearly, vertical repetitive projects involve the repeti-
tion of a unit network throughout the project in discrete steps. They
are therefore often referred to as discrete repetitive projects.
Examples are multiple similar houses and high-rise buildings.
Some repetitive construction projects include horizontal repetitive
processes and vertical repetitive processes together; Kang et al. (2001)
defined these as multiple repetitive projects. A typical example of such
projects is multi-story structures.
1.3 CHARACTERISTICS OF REPETITIVE ACTIVITIES AND
PROJECTS
As a special kind of project, repetitive construction projects have many
characteristics that nonrepetitive projects may not have, such as repetitive
and nonrepetitive activities, typical and non-typical activities, resource
continuity constraints, distance constraints, and hard and soft logic rela-
tions. These characteristics are described below to show the need for a
targeted scheduling technique and tool that must be able to model them.
1.3.1 Repetitive and Nonrepetitive Activities
Repetitive activities are those activities that need to be performed in
two or more units in the project. On the other hand, nonrepetitive activ-
ities are those activities whose sub-activities do not exist in more than
one unit. The most common situation is where an activity exists only
in the beginning of the project (before starting the first unit) and/or in
the first unit. For example, excavation is considered a nonrepetitive
activity for high-rise buildings in which it is required only prior to the
construction of the first unit (i.e., the first floor). Repetitive construction
projects can be made up of all repetitive activities or both repetitive and
nonrepetitive activities. Figure 1.1 is an example of a repetitive con-
struction project with nonrepetitive activities; its node network is shown
2 Repetitive Project Scheduling: Theory and Methods

in Figure 1.1(a) where the combinations of capital letters and numbers
represent the sub-activities of some activities in some units. For exam-
ple, “C2” means the sub-activity of activity C in unit 2. By definition,
activity A is a nonrepetitive activity, but activities B and C are repeti-
tive activities. The graphical scheduling technique in Figure 1.1(b) is
the repetitive scheduling method (RSM), in which the horizontal and
vertical axes represent production unit and time, respectively.
Sub-activities of an activity in each unit are represented by an oblique
line, and each unit is represented by two points: the first denotes the
unit start time, and the second denotes its finish time. The vertical
difference between the two points is the activity duration for that unit.
1.3.2 Typical and Non-Typical Activities
A typical activity is defined as a series of sub-activities that have the
same work amount and duration for each repetitive unit. In contrast, a
non-typical activity is a series of sub-activities having different work
amounts and, therefore, different durations in different units. If all the
activities of a project are typical activities, then the project is a typical
project; otherwise it is a non-typical one. Figure 1.2(a) and (b) demon-
strate examples of typical and non-typical projects, respectively.
Many scheduling techniques assume that the durations of sub-
activities are the same (typical), allowing one to solve the problem
easily. However, this assumption is not always practical since activity
duration is influenced by many factors such as work amount in each
A1
C1
0 1 2 3Unit
2
4
6
8
10
12
Days
B1
B3
C2
C3
Node network (b)
(a) RSM diagram
A1 B1 C1
B3
C2
C3
Sub-activity
Work sequence
between two sub-
activities
Figure 1.1 A repetitive construction project with repetitive and nonrepetitive activities.
3
Basic Concept

unit and resource productivity for each activity. The technique devel-
oped should be able to model both typical and non-typical activities.
1.3.3 Resource Continuity Constraints
For each repetitive activity, resource continuity constraints emphasize
keeping resources working continuously, without idle time. Idle time is
any period that resources are being paid out but not performing any
work. Since resources are paid from the date they start working to the
date they finish the work, idle time during employment periods is consid-
ered unproductive. Accordingly, activities should be scheduled in such a
way that idle time of resources is eliminated or minimized. Ensuring
resource continuity during scheduling also leads to (1) maximization of
the benefits from the learning curve effect for each crew; and (2) minimi-
zation of the off-on movement of crews on a project once work has
begun. However, Selinger (1980) thought that not all the activities of a
repetitive construction project should be required to meet the resource
continuity constraint. The author recognizes a trade-off in scheduling
repetitive construction projects: work interruption indeed results in an
increased direct cost because of the idle time of resources and therefore
needs to be avoided. But violation of these resource continuity constraints
by allowing work interruption may possibly lead to an overall project
duration reduction and corresponding indirect costs, and consequently, a
careful trade-off should be made between these two extremes.
A more intuitive comparison is shown in Figure 1.3. The project
duration of plan A, in which all the activities must meet the resource
A1
C1
0 1 2 3 Unit
2
4
6
8
10
12
Days
A2
A3
B1
B2
B3
C2
C3
A1
C1
0 1 2 3 Unit
2
4
6
8
10
12
Days
A2
A3
B1
B2
B3
C2
C3
(a) A typical project (b) A non-typical project
Figure 1.2 Typical and non-typical projects.

continuity constraint (Figure 1.3(a)) is equal to 11 days, and the
corresponding resource idle time is zero. On the other hand, in
Figure 1.3(b), the project duration of plan B is shortened by 2 days by
violating the resource continuity constraint, and it also creates 2 days
of idle resource time. Comparing these two plans, both have the same
direct project costs, since the durations of all the sub-activities are not
changed. At present, if the total cost for covering idle resources under
plan B is less than the project indirect cost of plan A, plan B is better
than plan A; otherwise, plan B is worse than plan A.
1.3.4 Distance Constraints
Distance constraints are of two types: maximum and minimum dis-
tance constraints. The minimum distance constraint indicates that two
activities cannot approach each other more than a specified length (or
unit) at any time during the project duration. For example, a tunnel’s
final lining cannot approach excavations more than a specified dis-
tance in order to work more effectively and for safety reasons. When
planning a vertical repetitive project, the minimum distance constraint
is used to ensure resource continuity from one unit/story to the next.
On the other hand, the maximum distance constraint indicates that
two activities cannot be further away from each other than a specified
distance. An example of such constraint may be “a pipe trench should
not be left without being backfilled for more than 500 m for safety
reasons.” Two activities can be linked with both a minimum and
maximum distance constraint.
A1
C1
0 1 2 3 Unit
2
4
6
8
10
12
Days
A2
A3
B1
B2
B3
C2
C3
(a) (b)
Schedule with the resource continuity constraint
A1
C1
0 1 2 3 Unit
2
4
6
8
10
12
Days
A2
A3
B1
B2
B3
C2
C3
Idle time
Idle time
Schedule without the resource continuity constraint
Plan A Plan B
Figure 1.3 Schedule with and without the resource continuity constraint.
5
Basic Concept

1.3.5 Hard and Soft Logic Relations
The work sequence between units of an activity is determined by the
character of logic relations. In practice, logic relations may be of a
“hard” or “soft” character. Hard logic is that inherent in the nature of
the work being done. It usually involves technological constraints and
often physical limitations (Kallantzis and Lambropoulos, 2004). If the
logic relation of an activity is hard, its work sequence between units
cannot be changed; for example, the steel structure of a high-rise build-
ing must be performed by the fixed sequence from bottom to top.
According to Tamimi and Diekmann (1988), soft logic consists of
those relations which allows activities to be scheduled by a variety of
work sequences or performed simultaneously in certain circumstances
(i.e., the relations are canceled). An example of soft logic in repetitive
construction project may be “perform excavation work in four units
by the sequence 1-2-3-4” (assumed by the planner); it is physi-
cally possible to “weaken” this relation to generate other optional
sequences, for example, “1-4-3-2” or “3-4-2-1.”
In some cases, hard logic is not a good representation of the logical
relations of activities, and may unnecessarily limit flexibility in scheduling
activities and allocating resources. For example, in Figure 1.4, a housing
project consisting of three houses, the sequence of construction for these
three houses is not constrained by technological constraints. Therefore,
the construction of these houses can be scheduled in many sequences, such
as units 1-2-3 as shown in Figure 1.4(b) or units 2-3-1 as shown in
Figure 1.4(c). In such a case, constraining repetitive units with hard logic
(forcing the sequence of the housing unit 1 3) would be unnecessary.
Soft logic is the ability of a crew to define its own sequences of units
for performing the repetitive work. A comparison of Figure 1.4(b) and
(c) shows the benefit of applying soft logic relations to the project. As
shown in Figure 1.4(c), reordering the housing units from units
1-2-3 to units 2-3-1 results in a project duration shorter by
2 weeks. Accordingly, the idea of soft logic and its benefits needs to be
studied further.
1.4 NETWORK PLANNING TECHNIQUES
Using rational planning and scheduling methods is one key to ensuring
the successful completion of a project. Network planning techniques

are methods based on graph theory to analyze, describe, structure,
plan, control, and steer projects and processes, whereby time, cost,
resources, and other influential factors can be taken into consideration.
The two basic network planning techniques are the critical path
method (CPM) and the plan evaluation and review technique (PERT).
1.4.1 Critical Path Method
CPM was developed in the 1950s by James Kelly and Morgan Walker
(Senior, 1993). The method offers an easy calculation to derive a project
schedule and to assess the criticality of activities using the concepts of
floats and the critical path, focusing on time. Activities and their prece-
dence relations are depicted in a network by nodes and arrows. Nodes
represent activities and activity information such as title, duration, etc.
A1
C1
0 1 2 3 Unit
4
8
12
16
20
Week
B3
A3
D2
D3
(b) RSM diagram 1
A2
Sub-activity
Precedence relation
B2 D2 E2
C2
A1 B1 D1 E1
C1
A3 B3 D3 E3
C3
Logic relation
A2
B1
C2
C3
D1
E3
E2
E1
A1
C1
0 2 3 1 Unit
4
8
12
16
20
Week
B1
A3
D2
D3
(c) RSM diagram 2
A2
B3
B2
C2
C3
D1
E3
E2
E1
(a) Node network
B2
Figure 1.4 A repetitive construction project with soft logic relations.
7
Basic Concept

Arrows represent the precedence relations between activities and the
lead time between them. After the network is constructed and the activ-
ity durations are given, the calculation of critical path, critical activities,
and floats can be performed straightforwardly. The information derived
informs project managers of the criticality of activities, which allows
them to plan in advance how to schedule the activities and manage the
project effectively, based on the current schedule. On the other hand,
the managers may decide to alter the original schedule to suit the project
deadline, the company resources, and so forth.
Although CPM has been widely used for planning, scheduling, and
controlling of construction projects since the late 1950s, it has been rec-
ognized as quite unsuitable for repetitive construction projects. The
main reasons include:
• It does not guarantee continuity of resources. Although it has been
reported by several authors that the uninterrupted utilization of
resources is an extremely important issue, neither CPM nor its
resource-oriented extensions take these resource continuity con-
straints into account.
• It does not show the location and time at which a certain crew will
be working on a given activity, so it is not efficient for visually
monitoring the progress of a particular crew. Moreover, when the
distance constraint between activities is violated, CPM cannot
provide feedback in time.
• It is believed to be inefficient for large-scale repetitive construction
projects, since its calculation becomes tedious and labor intensive
(Yang, 2002). For example, a repetitive project consisting of seven
activities for 1000 units will require 7000 nodes to represent the
network. A network of this size is confusing and unmanageable.
1.4.2 Plan Evaluation and Review Technique
PERT was developed in the late 1950s for the U.S. Navy’s Polaris
project, which involved thousands of contractors. It has the potential
to reduce both the time and cost required to complete a project. A dis-
tinguishing feature of PERT is its ability to deal with uncertainly in
activity durations. For each activity, the model usually includes three
time estimates:
• Optimistic time: generally the shortest time in which the activity can
be completed.

• Most likely time: the completion time having the highest probabil-
ity. This is different from expected time. Seasoned managers have
an amazing way of estimating very close to actual data from prior
estimation errors.
• Pessimistic time: the longest time that an activity might require.
However, PERT has not been widely used in the construction
industry compared to CPM, as it requires more data on activity dura-
tions, which is often difficult to obtain or justify. Moreover, PERT
requires intensive computation compared to CPM. From the perspec-
tive of a repetitive construction project, PERT and CPM have the
same limitations due to their underlying time-based scheduling calcula-
tion and their graphical presentation in precedence networks.
1.5 EXISTING SCHEDULING TECHNIQUES FOR REPETITIVE
CONSTRUCTION PROJECTS
Instead of time-driven techniques (e.g., CPM and PERT), resource-
driven techniques have been used to schedule repetitive construction
projects such that distance and resource continuity constraints are met
and spatial information is shown. These techniques include, but are
not limited to:
• Line-of-balance (LOB); see Carr and Meyer (1974), Arditi and
Albulak (1986), Al Sarraj (1990), Wang and Huang (1998). LOB is
a variation of linear scheduling methods that allows the balancing
of operations such that each activity is performed continuously. The
major benefit of the LOB methodology is that it provides produc-
tion rate and duration information in the form of an easily inter-
preted graphical format. The LOB plot can show at a glance what is
wrong with the progress of an activity, and can detect potential
future bottlenecks (Arditi et al., 2002).
• Vertical production method (VPM); see O’Brien (1975), Suhail and
Neale (1994). VPM is used to schedule the repetitive floors of a
high-rise building in conjunction with CPM for non-standard floors.
The VPM is essentially a LOB technique tailored to high-rise build-
ings. Each repetitive floor is modeled as a unit network; the schedule
is then created using VPM. The number of crews on a specific activ-
ity is adjusted to provide production rates that balance with other
activities.
9
Basic Concept

• Horizontal and vertical logic scheduling for multi-story projects; see
Thabet and Beliveau (1994). Resources that are considered for
scheduling are the physical space requirements of material storage
and the movement of manpower and equipment. The scheduling
actions proposed to allocate the space resource are: (1) adjustment
of productivity rates, (2) interruption of the flow of the activity, and
(3) delay in the start of the activity.
• Linear scheduling method (LSM); see Johnston (1981),
Chrzanowski and Johnston (1986), Harmelink and Rowings (1998).
LSM has long been regarded as a technique that provides significant
advantages when applied to linear projects. A linear schedule with
time on the horizontal axis and location on the vertical is presented,
with activities represented by lines and the slope representing the
production rate.
• RSM; see Harris and Ioannou (1998), Zhang and Qi (2012). RSM is
similar to LSM; the main difference is that the time constraints in
RSM limit the start and finish times of two sub-activities in the
same unit by a specified “lag time” or “lead time,” but the time con-
straints in LSM limit the performance time of two activities at the
same location by specified maximum or minimum time buffers.
Generally speaking, RSM is more adaptable to scheduling discrete
projects such as housing projects.
All of the methods described above involve two dimensions: time
and location (or unit). They can be classified into two groups: LOB
and RSM; the former will be described in detail in Chapter 2, while
the latter, as the main planning and scheduling tool in this book, will
be introduced in Chapter 3.

CHAPTER 2
2
Line-of-Balance Technique
2.1 INTRODUCTION
Line-of-balance (LOB) is a technique developed in the 1950s by the
U.S. Navy to monitor production-type projects where the delivery of
an item is monitored. As a resource-driven technique, the major objec-
tive of LOB is to achieve a resource-balanced schedule by determining
the suitable crew size and number of crews to employ in each repetitive
activity. The major benefit of LOB methodology is that it presents
production rate and duration information in an easily interpreted
graphical format (Yang and Ioannou, 2004). The LOB plot can pres-
ent at a glance the progress rate of activities, allowing the possibility to
adjust the rates to meet project deadlines, while maintaining work
continuity of resources.
Because LOB assumes essentially sequential activities, efforts have
been made to combine the benefits of critical path method (CPM) and
LOB techniques. One notable effort in this field is the model developed
by Suhail and Neale (1994) as a framework for CPM-LOB integration.
Their procedure was the first approach to offer a formula for determin-
ing crews needed to meet a given deadline. Activities’ total float values
are used to relax noncritical activities without impacting the project
completion date. However, the framework works well only when the
calculated number of crews is not rounded to integer numbers.
Moreover, it does not consider resource constraints. Since then, more
studies have focused on the integration of LOB and CPM methodolo-
gies, including studies by Hegazy and Wassef (2001), Ammar and
Mohieldin (2002), Hegazy (2002), and Ammar (2013).
In this chapter, a basic definition and graphical representation
of LOB will be introduced. Then the successive steps of an inte-
grated CPM-LOB method will be elaborated. Finally, the disad-
vantages of the LOB technique and future research directions will
be discussed.

2.2 BASIC CONCEPT AND REPRESENTATION
The most common representation format of LOB is shown in
Figure 2.1, in which each bar represents one activity and each repeti-
tive unit is represented by a horizontal line. The width of the bar is the
activity duration of one unit, which is assumed to be uniform across
all units. This assumption is not true but it is realistic, especially in
projects with a large number of repetitive units. The intersections of a
horizontal line at any unit and the activity bar represent the start and
finish time for this activity in that unit, respectively.
2.2.1 Crew Synchronization
The representation of LOB allows for multiple crews to be used in the
same activity. When several crews are involved in one activity, the LOB
schedule assigns tasks for these crews in a regular method, in order to
achieve crew synchronization. The specific allocations are: (1) unit 1 is
completed by crew 1; and (2) if the work of the jth unit is assigned to
crew t, unit j 1 1 is completed by crew t 1 1; however, if crew t is the last
crew, unit j 1 1 is completed by crew 1, as shown in Figure 2.1.
2.2.2 Optimum Crew Size and Natural Rhythm
In LOB, the principle of “optimum crew size” assumes that the highest
productivity can be achieved as long as an activity is performed in a
unit of production by a crew of optimum size. Any crew that is
composed of either fewer or more workers is bound to result in lower
productivity, as shown in Figure 2.2. The principle of “natural rhythm”
0
1
2
3
4
5
6
Crew 1
Crew 2
Crew 1
Crew 2
Time
Units
Crew 1
Crew 2
Start
Finish
Figure 2.1 Basic representations of repetitive activities.

implies that to increase the progress rate of an activity, multiple crews
with optimum size must be employed, such that no idle time occurs
when crews move from one unit to another. Consider a U-unit activity;
its duration for one unit is D days when the optimum crew size is
reached. Then the progress rate of this activity that can meet natural
rhythm can only be C/D, where C denotes the number of crews
employed.
For a thorough discussion of optimum crew size and natural
rhythm, readers are directed to Lumsden (1968), Arditi and Albulak
(1986), and Arditi et al. (2002). It may seem difficult to implement the
principles of “optimum crew size” and “natural rhythm” in real-life
construction projects. However, many construction companies keep
records of worker-hours, crew sizes, and daily working hours in previ-
ously completed projects. Contractors can estimate the optimum crew
size for an activity using this information.
2.3 INTEGRATED CPM-LOB METHOD
The objective of LOB is to achieve a resource-balanced schedule by
determining the number of crews to be employed in each repetitive
activity. This is conducted such that the units are delivered at a rate
that meets a pre-specified deadline and crews’ resource continuity is
maintained. The analysis also involves determining the start and finish
times of all activities in all units and the crews’ assignments.
1 2 3 4
20
40
60
80
100
120
140
Crew size (number of workers)
Productivity
(required
worker-hours)
Figure 2.2 The relationship between required worker-hours and crew size.
13

The method consists of three main components, which are discussed in
the following subsections.
2.3.1 Meeting a Given Deadline
As shown in Figure 2.3, the end of the project (time TL) is the date at
which the last activity in the last unit is finished. When the first unit of
the project is finished, at time T1, the remaining time until the deadline
is taken to complete the remaining N 2 1 units (N is the number of
repetitive units). Accordingly, to meet the given deadline, a desired
rate of progress (R) can be calculated as follows:
R 5
N 2 1
TL 2 T1
(2.1)
where TL is the deadline of the project and T1 is the CPM duration of
the first unit.
Suhail and Neale (1994) suggested a modification to Eq. (2.1) in order
to include noncritical activities such that these activities can be relaxed
and given slower rates, taking into consideration the activities’ total float.
Accordingly, the progress rates were modified as shown in Eq. (2.2).
Ri 5
N 2 1
TL 2 T1 1 TFi
(2.2)
where Ri is the progress rate of activity i, and TFi is the total float of
activity i.
Time
Unit
T1 = CPM duration of unit 1
TL = given project deadline
N–1
N
1
2
R
Figure 2.3 Desired project rate of delivery.

The progress rate determined from Eq. (2.2) is, in fact, the mini-
mum progress rate of activity i for meeting the given deadline. In other
words, if the progress rate of activity i is less than Ri calculated by
Eq. (2.2), then no matter how many crews are employed for other
activities, the project cannot be finished within the given deadline.
2.3.2 Number of Crews Determination
When the progress rate is determined, the number of crews (Ci) for the
activity can be determined using Eq. (2.3). In general, the number of
crews calculated by Eq. (2.3) may not an integer value, and fractional
crews are not possible. Therefore, the number of crews must be
rounded up to determine the actual number of crews (Cai), as given by
Eq. (2.4a). Equation (2.4b) ensures that the actual number of crews
allocated to an activity does not exceed crew availability for that
activity. Consequently, the actual progress rates (Rai) for different
activities must be recalculated, with reference to Figure 2.4, by
Eq. (2.5). Equation (2.5) also means that resource continuity is
achieved by shifting the start of each unit from its previous one by a
time Di=Cai or 1=Rai. This shift also has a practical meaning. Because
each crew has part of its duration non-shared with other crews, the
chances of work delay are reduced when two crews need the same
resource, such as a crane.
1
2
3
4
5
6
Crew 1
Crew 1
Crew 2
Crew 3
Time
Units
Crew 3
Crew 2
Di/Cai
Cai = 3
Rai
Di/Cai Di/Cai
Figure 2.4 Synchronization and resource continuity of crews.
15

Ci 5 Di 3 Ri (2.3)
where Di is duration of activity i in one unit.
Cai 5 rounded upðCiÞ (2.4a)
Cai # the maximum available crews of activity i (2.4b)
Rai 5 Cai=Di or Di=Cai 5 1=Rai (2.5)
2.3.3 Drawing LOB Schedule
The resulting LOB schedule becomes simple to draw if all activities
run exactly at the desired progress rate Ri without rounding of crews.
Otherwise, those activities which need to round up the number of
crews will see a greater progress rate than in a theoretical sense. This
may lead to delay of the project if resource continuity is to be main-
tained. In this case, the original schedule will need to be amended.
A simple approach is to reschedule the project with a deadline that is
slightly shorter than originally desired. In general, however, redrawing
the schedule should be done carefully.
In working out the LOB schedule using the actual rate of progress
of activities, it is necessary to comply with the precedence relations
among activities. When an activity is considered, its predecessors are
examined first to identify their latest finish times, which are then con-
sidered as a boundary on the start of the current activity. Also, in
terms of presentation, showing all the activities on the same chart
results in a crowded schedule and can be confusing, even for a small
network. To solve this problem, a feasible method is to draw the criti-
cal paths in one chart and show the other noncritical paths in another
chart. The benefit of drawing these paths is to help visualize the succes-
sor and predecessor relations for any given task and accordingly facili-
tate any desired changes to rates or crews. However, this method has a
significant disadvantage: it does not apply to large-scale projects, and
when the number of crews on an activity changes, it will be harder to
update all charts. Once the schedule is drawn, the start and finish times
for each unit in each activity can be read and crew assignments shown.
2.3.4 Example Application
Steps and features of the integrated CPM-LOB method are demon-
strated by an example application with 10 identical units. The desired
contract duration is 40 days and a minimum buffer time of one day is

to be maintained between consecutive activities. The activities involved
in the construction of one unit of the project are given, together with
their estimated durations, in Table 2.1.
The example application is solved manually, applying the integrated
CPM-LOB method, in the following steps:
• Perform CPM analysis for the first unit, considering unit duration
of each activity and a minimum buffer time of one day. Figure 2.5
shows the CPM calculations for a single unit of the project, where
the one-day buffer is set as a lag time between activities. The result-
ing CPM duration for the first unit (T1) is 15 days and the critical
path is 1-2-4-5-6. The total float values of noncritical activities are
given in Table 2.2.
• Calculate the actual progress rate of each activity. Because the
desired project duration (TL) is 40 days, the desired progress rate
of progress (R) can be calculated using Eq. (2.1) as
ð10 2 1Þ=ð40 2 15Þ 5 0:36. The progress rate of noncritical activities
is calculated considering total float using Eq. (2.2). The theoretical
and actual number of crews, as well as actual progress rate of each
activity, are calculated and are also given in Table 2.2.
Table 2.1 Date for the Example Application
Activity Number Description Duration (days) Preceding Activities
1 Locate and clear 1
2 Excavate 3 1
3 String pipe 1 1
4 Lay pipe 4 2,3
5 Pressure test 1 4
6 Backfill 2 5
0 1
0 1
1 (1)
2 5
2 5
2 (3)
6 10
6 10
4 (4)
11 12
11 12
5 (1)
2 3
2 3
3 (1)
ES EF
LS LF
Act. No.
(duration)
ES: earliest start time
EF: earliest finish time
LS: latest start time
LF: latest finish time
13 15
13 15
6 (2)
1 1 1
1 1
1
Figure 2.5 CPM calculations for the example application.
17

• Draw the LOB schedule. Because there is no preceding activity for
activity 1, it starts at time zero. The actual number of crews for this
activity is 1, and its unit duration is 1 day. Thus, the last unit of activ-
ity 1 will be finished in the 10th day. The succeeding activities of
activity 1 include activities 2 and 3, and their actual progress rates are
not larger than 1. Then, the start times of both activities 2 and 3 in
the first unit are equal to the summation of the finish time of activity
1 in the first unit and the buffer time of 2 days. Meanwhile, the finish
times of activities 2 and 3 in the last unit are determined by their start
times in the first unit and their actual numbers of crews, respectively.
The resulting LOB diagram is shown in Figure 2.6. The start and
finish times of each unit in each activity are given in Table 2.3.
2.4 COMMENTS AND FUTURE RESEARCH
The existing LOB technique is a heuristic procedure, since it cannot
ensure that the deadline constraint is always satisfied. Take the project
in the previous section as an example: the given deadline is 40 days,
but the actual project duration obtained by the LOB calculation is 42
days. The common solutions for further shortening the project dura-
tion are: (1) increase or decrease the number of crews of some activities
to improve or lower their progress rates; and (2) allow those activities
with higher progress rates to be interrupted. In future studies, improve-
ments of LOB techniques can be considered in the following ways:
• Integrate the timecost trade-off analysis into LOB scheduling.
When scheduling a project, planners always attempt to look for the
Table 2.2 Line-of-Balance Calculations for the Example Application
No. Duration
Di
Total
Float
TFi
Actual Progress
Rate Ri 5 9/
(25 1 TFi)
Theoretical
Number of
Crews
Ci 5 DiRi
Actual Number of
Crews Cai 5 rounded
up Ci
Actual
Progress
Rate
Rai 5 Cai/Di
1 1 0 0.36 0.36 1 1
2 3 0 0.36 1.08 2 0.667
3 1 2 0.333 0.333 1 1
4 4 0 0.36 1.44 2 0.5
5 1 0 0.36 0.36 1 1
6 2 0 0.36 0.72 1 0.5

optimal balance between time and cost for the project to be built. In
LOB scheduling, the direct cost of an activity is proportional to the
number of crews employed in this activity. The employment of
more crews indeed results in a faster progress rate but obviously at
an increased direct cost. On the other hand, violation of the resource
continuity constraint by allowing work interruption may lead to an
overall project duration extension but decrease the corresponding
idle resource costs. In order to determine the optimum number of
crews and interruption strategies for all activities so as to yield the
minimum project cost while complying with a given deadline
10 20 30 40
0
1 2 3 4 5 6
Time
Unit
Figure 2.6 Line-of-balance diagram for the example application.
Table 2.3 Start and Finish Times for Each Sub-Activity
Activity 1 2 3 4 5 6
Timing ST FT ST FT ST FT ST FT ST FT ST FT
1 0 1 2 5 2 3 6 10 20 21 22 24
2 1 2 3.5 6.5 3 4 8 12 21 22 24 26
3 2 3 5 8 4 5 10 14 22 23 26 28
4 3 4 6.5 9.5 5 6 12 16 23 24 28 30
5 4 5 8 11 6 7 14 18 24 25 30 32
6 5 6 9.5 12.5 7 8 16 20 25 26 32 34
7 6 7 11 14 8 9 18 22 26 27 34 36
8 7 8 12.5 15.5 9 10 20 24 27 28 36 38
9 8 9 14 17 10 11 22 26 28 29 38 40
10 9 10 15.5 18.5 11 12 24 28 29 30 40 42
19

constraint, existing LOB techniques needs to be improved to have
the ability to balance time and cost.
• Take the learning effect into consideration. Traditional LOB techni-
ques assume that the production rate of an activity at each unit is
constant. However, in many realistic applications, workers can
improve their productivity with experience and practice (Lam et al.,
2001; Jarkas, 2010; Pellegrino et al., 2012). As a result, the time and
resources expended to complete the work on a unit will decrease as
the number of repetitions increases. This phenomenon is known
as “the learning effect” in the literature (Badiru, 1992). Considering
the learning effect when planning and scheduling a project helps
provide a realistic forecast of its duration and cost. This brings a
higher degree of precision in budgeting and schedule, and can foster
more competitive bidding. Thus, it is necessary to take the learning
effect into consideration in LOB scheduling.
• Consider non-typical and nonrepetitive activities. Repetitive or
linear construction, though it is characterized as a project of a repet-
itive nature, may contain some nonlinear and nonrepetitive
activities. A non-typical activity is characterized by repetitive opera-
tions, where the output of operations is not uniform at every unit.
For example, in a highway project, the workload of earthwork will
vary from section to section, simply due to differences in the terrain.
A nonrepetitive activity, on the other hand, is a one-off activity that
does not repeat itself in every unit. An example of a nonrepetitive
activity in a highway paving project is the posting of the occasional
sign structure. Non-typical activities cannot be treated like typical
and repetitive activities in LOB calculations because the outputs in
these activities differ from unit to unit. The nonrepetitive portions
of a project cannot be scheduled directly by the LOB method either,
because these activities are not included in the CPM network of the
first unit. Yet both non-typical and nonrepetitive activities may
interfere with the scheduling of adjacent activities and, conse-
quently, with the critical path. Therefore, the schedule for the entire
project cannot be produced until these nonlinear and nonrepetitive
activities are scheduled and coordinated with the typical and repeti-
tive activities. There should therefore be a mechanism that allows
the scheduler to accommodate non-typical and nonrepetitive
activities in an LOB schedule (Arditi et al., 2002).

2.5 CONCLUSION
LOB is one of the most common tools for scheduling repetitive con-
struction projects. The advantages lie in its ability to display progress
rates and duration information for all activities in the LOB diagram.
Executing LOB calculations aims to find a schedule that can satisfy
the given deadline and resource continuity constraints for typical pro-
jects. Under some circumstances, the project duration obtained by the
LOB calculation will be longer than the given deadline. At that point,
the original schedule will need to be amended. Possible methods
include (1) increasing (or decreasing) the number of crews of some
activities, and (2) allowing some activities to be interrupted.
LOB is a scheduling tool waiting to be improved. The main limita-
tions are: (1) it cannot perform a timecost trade-off analysis; (2) it
ignores the learning effect of workers by assuming the productivities of
all crews remain unchanged; and (3) it cannot accommodate non-
typical and nonrepetitive activities in an LOB schedule. These
disadvantages greatly limit the application of LOB techniques in actual
projects.
21

CHAPTER 3
3
Controlling Path Analysis in Repetitive
Scheduling Method
3.1 INTRODUCTION
The controlling path, also known as the controlling activity path or
controlling sequence, is defined as the longest continuous path from
project start to project completion, which determines the minimum
project duration under certain conditions (such as the crews that deter-
mine the production rate) and requirements (such as the constraints of
precedence relations). The segments on the controlling path are named
controlling segments, and the constraints (precedence relations) on the
controlling path are named controlling constraints.
Harmelink and Rowings (1998) put forward a method for determin-
ing the controlling path of linear projects by upward pass and down-
ward pass. The goal of the upward pass is to determine which
activities or portions of activities could potentially be controlling. The
process starts with the beginning of the project and progresses upward.
In each step, the activity for which the potential controlling sub-
activity is being determined is designated the origin activity, and
the earliest point in time for this activity is designated as the origin. The
next activity in the activity sequence list will be the target activity.
The least distance interval describes the location at which this closest
point occurs. Once the least distance interval has been determined,
the point of intersection with the origin activity is called the critical
vertex. The sub-activity of the origin activity between the origin and the
critical vertex is then a potential controlling sub-activity for this activity,
and the least distance interval becomes a potential controlling link
between the origin and target activities. The target activity in this step
of the upward pass becomes the origin activity for the next step, and the
process repeats until all of the potential controlling activity segments
have been determined. On the other hand, the purpose of the down-
ward pass is to determine which portions of the potential controlling
sub-activities are actually on the controlling path. This step can be

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The Project Gutenberg eBook of The Devil-
Tree of El Dorado: A Novel

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Title: The Devil-Tree of El Dorado: A Novel
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[Page 249.
“IT WAS PASSED ABOUT; NOW LIFTED HIGH IN THE AIR BY ONE END,
THEN BY THE OTHER.”
Frontispiece.]

The Devil-tree
of El Dorado
A Novel
BY
FRANK AUBREY
WITH ILLUSTRATIONS BY LEIGH ELLIS AND
FRED. HYLAND.
NEW YORK
NEW AMSTERDAM BOOK COMPANY
156 FIFTH AVENUE
LONDON: HUTCHINSON COMPANY
Copyright, 1897,
by
NEW AMSTERDAM BOOK COMPANY.

S
PREFACE.
SHALL RORAIMA[1] BE GIVEN UP TO VENEZUELA?
HALL Roraima be handed over to Venezuela? Shall the
mysterious mountain long known to scientists as foremost
among the wonders of our earth—regarded by many as the greatest
marvel of the world—become definitely Venezuelan territory?
This is the question that hangs in the balance at the time these
words are being written, that is inseparably associated—though
many of the public know it not—with the dispute that has arisen
about the boundaries of British Guiana.
Ever since Sir Robert Schomburgk first explored the colony at the
expense of the Royal Geographical Society some sixty years ago,
Roraima has remained an unsolved problem of romantic and
fascinating interest, as attractive to the ‘ordinary person’ as to the
man of science. And to those acquainted with the wondrous
possibilities that lie behind the solution of the problem, the prospect
of its being handed over to a country so little worthy of the trust as
is Venezuela, cannot be contemplated without feelings of
disappointment and dismay.
This is not the place in which to give a long description of
Roraima. It will suffice here to say that its summit is a table-land
which, it is believed, has been isolated from all the rest of the world
for untold ages; no wilderness of ice and snow, but a fertile country
of wood and stream, and, probably, lake. Consequently it holds out
to the successful explorer the chance—the probability even—of
finding there hitherto unknown animals, plants, fish. In this respect
it exceeds in interest all other parts of the earth’s surface, not
excepting the polar regions; for the latter are but ice-bound wastes,
while Roraima’s mysterious table-land lies in the tropics but a few
degrees north of the equator.

Why, then, it may be asked, have our scientific societies not
exhibited more zeal in the solving of the problem presented by this
strange mountain? Why is it that unlimited money can, apparently,
be raised for expeditions to the poles, while no attempt has been
made to explore Roraima? Yet, sixty years ago, the Royal
Geographical Society could find the money to send Sir Robert
Schomburgk out to explore British Guiana—indeed, it is to that fact
that we owe the discovery of Roraima—but nothing has been done
since. Had the good work thus begun been followed up, we should
to-day have been able to show better reason for claiming Roraima as
a British possession. But, as the writer of the article in the Spectator
quoted on page 3 says, “we leave the mystery unsolved, the marvel
uncared for.” This article is commended to the perusal of those
interested in the subject, as also are the following books, which give
all the information at present available, viz.—Mr. Barrington Brown’s
‘Canoe and Camp Life in British Guiana,’ and Mr. Boddam-Whetham’s
‘Roraima and British Guiana.’ Mr. Im Thurn’s ‘Among the Indians of
British Guiana’ should also be mentioned, since it contains
references to Roraima, though the author did not actually visit the
mountain, as in the case of the first named.
As an illustration of the confusion and uncertainty that prevail as
to the international status of this unique mountain, it may be
mentioned that in the map of British Guiana which Sir Robert
Schomburgk drew out for the British Government, it is placed within
the British frontier. But in the map of the next Government explorer,
Mr. Barrington Brown—‘based,’ he says, ‘upon Schomburgk’s map’—it
is placed just inside the Venezuelan boundary; and no explanation is
given of the apparent contradiction. Again, another authority, Mr. Im
Thurn (above referred to), Curator of the Museum at Georgetown
(the capital of the colony), in his book says that Roraima “lies on the
extreme edge of the colony, or perhaps on the other side of the
Brazilian boundary.” These references show the obscurity in which
the whole matter is at present involved.
Apart, however, from the special interest that surrounds Roraima
owing to the inaccessible character of its summit,[2] it is of very

great geographical importance, from the fact that it is the highest
mountain in all that part of South America, i.e., in all the Guianas, in
Venezuela, and in the north-east part of Brazil. Indeed, we must
cross Brazil, that vast country of upwards of three million square
miles, to find the nearest mountains that exceed in height Roraima.
Consequently, it forms the apex of the water-shed of that part of
South America; and it is, in fact, the source of several of the chief
feeders of the great rivers Essequibo, Orinoco and Amazon.
Schomburgk, in pointing this out, dwelt strongly upon the
importance of the mountain to British Guiana, and insisted that its
inclusion within the British boundary was a geographical necessity.
Finally, Sir Robert’s brother, Richard Schomburgk, a skilled
botanist, who had visited almost all parts of Asia and Africa in search
of orchids and other rare botanical productions, tells us that the
country around Roraima is, from a botanical point of view, one of the
most wonderful in the world. “Not only the orchids,” he says, “but
the shrubs and low trees were unknown to me. Every shrub, herb
and tree was new to me, if not as to family, yet as to species. I
stood on the border of an unknown plant zone, full of wondrous
forms which lay as if by magic before me.... Every step revealed
something new.” (‘Reissen in Britisch Guiana,’ Leipzig, vol. ii., p. 216.)
Are our rulers, in their treatment of the question, bearing these
facts sufficiently in mind? Are they as keenly alive as are the
Venezuelans to the importance of Roraima? If they are, there is no
sign of it; for while, in the Venezuelan statements of their case,
there are lengthy, emphatic, and repeated references to the
importance of Roraima, on the English side—in the English press
even—there is scarcely a word about it.
From these observations it will be seen that there is reason to fear
we may be on the point of allowing one of the most scientifically
interesting and geographically important spots upon the surface of
the globe to slip out of our possession into that of a miserable little
state like Venezuela, where civil anarchy is chronic, and neither life
nor property is secure.

One of the avowed objects of this book, therefore, is to stimulate
public interest, and arouse public attention to the considerations that
actually underlie the ‘Venezuelan Question,’ as well as to while away
an idle hour for the lovers of romance.
It has been suggested that, if it is too late to retain the wonderful
Roraima as exclusively British—and to effect this it would be well
worth our while to barter away some other portion of the disputed
territory—then an arrangement might be come to to make it neutral
ground. Standing, as it does, in the corner where the three countries
—Brazil, Venezuela and British Guiana—meet, it is of importance to
all three, and, no doubt, in such an endeavour, we should have the
support of Brazil as against Venezuela.
With regard to the oft-discussed question of the situation of the
traditional city of Manoa, or El Dorado—as the Spaniards called it—
most authorities, including Humboldt and Schomburgk, agree in
giving British Guiana as its probable site. We are told that it stood on
an island in the midst of a great lake called ‘Parima’; but no such
lake is now to be found in South America anywhere near the locality
indicated. An explanation of the mystery, however, is afforded by the
suggestion that such a great lake, or inland sea, almost certainly
existed at one time in precisely this part of the continent; in that
case what are now mountains in the country would then have been
islands.
Indeed, most of British Guiana lies somewhat low, and it is
estimated that if the highlands were to sink two thousand feet the
whole country would be under water—the mountain summits
excepted—and there would then be only ‘a narrow strait’ between
the Roraima range and the Andes. In this great supposed ancient
lake the group of islands now represented by mountain summits
might well have been the home of a powerful and conquering race—
as is to-day Japan with its group of more than three thousand
islands—and Roraima, as the highest, and therefore the most easily
defensible, may very well have been selected as their fastness, and
the site of their capital city.

Schomburgk thus states his speculations upon the point, in his
book on British Guiana, page 6:—
“The geological structure of this region leaves but little doubt that
it was once the bed of an inland lake which, by one of those
catastrophes of which even later times give us examples, broke its
barriers, forcing for its waters a path to the Atlantic. May we not
connect with the former existence of this inland sea the fable of the
lake Parima and the El Dorado? Thousands of years may have
elapsed; generations may have been buried and returned to dust;
nations who once wandered on its banks may be extinct and exist no
more in name; still, tradition of Parima and the El Dorado survived
these changes of time; transmitted from father to son, its fame was
carried across the Atlantic and kindled the romantic fire of the
chivalric Raleigh.”
As a natural sequence to the foregoing arises the inquiry, What
sort of people were those who inhabited this island city, or who
‘wandered on the banks’ of the great lake? Here much is to be
learned from the recent discoveries of the Government of the United
States who, of late years, have devoted liberal sums to pre-historic
research. The money so expended has been the means of
unearthing evidence of a startling character—relics of a former
civilisation that existed in America ages before the time of its
discovery by Christopher Columbus. The Spaniards, as we know,
found races that were white, or nearly so; but these later discoveries
go to show that long anterior to these—at a time, in fact, probably
coeval with what we call the Egyptian civilisation—America was
peopled with a white race fully as cultured, as advanced in the
sciences, and as powerful on their own ground as the ancient
Egyptians; and as handsome in personal appearance—if some of the
heads and faces on the specimens of pottery may be accepted as
fair examples—as the ancient Greeks.
It has long been known that America possesses extraordinary
relics of a former civilisation in what are known as the great
‘earthworks,’ which are still to be seen scattered about in many parts

of the continent, and which, as vast engineering works, challenge
comparison with the pyramids themselves. But now discovery has
gone much further; bas-reliefs and pottery have been found that set
forth with marvellous fidelity many minute details concerning this
pre-historic people—their personal appearance, and their ornaments
and habiliments; the style of wearing the hair and the beard; and
other particulars that can be appreciated only by inspection and
study of the reduced fac-similes lately printed and issued by the
Government of the United States.
Many of them relate to the custom of human sacrifice which, as
most people are probably aware, prevailed largely in America when
the Spaniards first landed there; though few, perhaps, know the
terrible extent to which it was carried. Prescott tells us that few
writers have ventured to estimate the yearly number of victims at
less than twenty thousand, while many put it as high as fifty
thousand, in Mexico alone! If we consider that the lowest of these
estimates represents an average of some four hundred a week, or
nearly sixty a day, such figures are appalling! And now we learn,
beyond the possibility of a doubt, that the same practices obtained
in America in times that must have been ages before the Spanish
conquest, and, judging by the frequency of the representations of
such things in these old bas-reliefs, as extensively. In these
sculptures we can see the very shape of the knives used; the form
of the plates or platters on which severed heads of victims were
placed, and other such details; and in a certain series we are
enabled to note the curious point, that, while the officiating priests
always wear full beards, the victims appear to have usually
possessed no hirsute adornments, or to have ‘shaved clean,’ as we
term it. It may be added that these ancient white people seem to
have been a totally different race from those the Spaniards found on
the continent; and that between the two there is believed to have
been a gap lasting for many ages, during which the country was
overrun by Indian or other barbaric hordes; though how or why this
came about is one of those mysteries that will probably never be
unravelled.

In conclusion, I have to acknowledge my indebtedness to the
writers whose books of travel I have named for the information I
have made use of; as well as to express a hope that the writer of
the review in the Spectator will regard with indulgence the liberties I
have taken with his admirable article. I am sanguine enough to
believe, however, that I shall have the sympathy and good wishes of
all these in the endeavour here made to arouse public attention to
the real meaning and importance of the ‘Venezuelan Question’; and
to add to the number of those who feel an interest in the future
status and ultimate exploration of the mysterious Roraima. I wish
also to express my thanks to Messrs. Leigh Ellis and Fred Hyland,
the artists to whom the illustrations were entrusted, for the thought
and care they have bestowed upon the work, and the successful
manner in which they have carried out my conceptions.
For the rest—if objection be taken to the accounts of the mountain
and what is to be found on its summit given by the characters in my
story—I desire to claim the licence of the romance-writer to maintain
their accuracy—till the contrary be proved. If this shall serve to
stimulate to renewed efforts at exploration, so much the better, and
another of my objects in writing the book will thereby have been
attained.
FRANK AUBREY.
[1] The Indians of British Guiana pronounce this word Roreema.
[2] Mr. Barrington Brown says the mountain can only be
ascended by means of balloons (see article previously referred to
on page 3); and Mr. Boddam-Whetham came to the same
conclusion.

CONTENTS.
CHAPTER I. PAGE
“WILL NO ONE EXPLORE RORAIMA?” 1
CHAPTER II.
MONELLA 17
CHAPTER III.
THE JOURNEY FROM THE COAST 26
CHAPTER IV.
THE FIRST VIEW OF RORAIMA 36
CHAPTER V.
IN THE ‘DEMONS’ WOOD’ 45
CHAPTER VI.
THE MYSTERIOUS CAVERN 58
CHAPTER VII.
THE CANYON WITHIN THE MOUNTAIN 70
CHAPTER VIII.
ALONE ON RORAIMA’S SUMMIT 79
CHAPTER IX.
VISION OR REALITY? 88
CHAPTER X.
IN SIGHT OF EL DORADO! 98
CHAPTER XI.
ULAMA, PRINCESS OF MANOA 106
CHAPTER XII.
A PRELIMINARY SKIRMISH 119
CHAPTER XIII.
A KING’S GREETING 129
CHAPTER XIV.
DAKLA 141

CHAPTER XV.
MARVELS OF MANOA 153
CHAPTER XVI.
LEONARD AND ULAMA 167
CHAPTER XVII.
THE FIGHT ON THE HILLSIDE 177
CHAPTER XVIII.
THE LEGEND OF MELLENDA 188
CHAPTER XIX.
HOPES AND FEARS 199
CHAPTER XX.
THE MESSAGE OF APALANO 210
CHAPTER XXI.
THE GREAT DEVIL-TREE 221
CHAPTER XXII.
SMILES AND TEARS 236
CHAPTER XXIII.
THE DEVIL-TREE BY MOONLIGHT 246
CHAPTER XXIV.
TRAPPED! 256
CHAPTER XXV.
‘IN THE DEVIL-TREE’S LARDER’ 268
CHAPTER XXVI.
CORYON 282
CHAPTER XXVII.
ON THE ‘DEVIL-TREE’S LADLE’ 290
CHAPTER XXVIII.
RALLYING TO THE CALL 301
CHAPTER XXIX.
‘THOU ART MY LORD MELLENDA!’ 308
CHAPTER XXX.
A TERRIBLE VENGEANCE 317
CHAPTER XXXI.

‘THE SON OF APALANO!’ 327
CHAPTER XXXII.
THE TREE’S LAST MEAL 339
CHAPTER XXXIII.
THE LAST OF THE GREAT DEVIL-TREE 350
CHAPTER XXXIV.
A MARRIAGE AND A PARTING 360
CHAPTER XXXV.
JUST IN TIME! 369
CHAPTER XXXVI.
THE END 382

LIST OF ILLUSTRATIONS.
“IT WAS PASSED ABOUT; NOW LIFTED HIGH IN THE AIR BY
ONE END, THEN BY THE OTHER” Frontispiece
“THERE BEFORE THEM ... THEY SAW THE MYSTERIOUS
RORAIMA” To face page 39
“A SCENE THAT WAS GRATEFULLY REFRESHING” „ „ 72
“THE SUN WAS JUST HIGH ENOUGH TO LIGHT UP THE
GLISTENING TOWERS AND CUPOLAS” „ „ 106
“SHE STOOD REGARDING THEM WITH WONDERING LOOKS” „ „ 115
“OTHER BRANCHES SWOOPED DOWN, COILING ROUND HIM” „ „ 252
“HE WAS STANDING WITH ONE ARM EXTENDED” „ „ 286
ON THE DEVIL-TREE’S LADLE „ „ 297
THE
DEVIL-TREE OF EL DORADO.

B
CHAPTER I.
“WILL NO ONE EXPLORE RORAIMA?”[3]
ENEATH the verandah of a handsome, comfortable-looking
residence near Georgetown, the principal town of British Guiana,
a young man sat one morning early in the year 1890, attentively
studying a volume that lay open on a small table before him. It was
easy to see that he was reading something that was, for him at
least, of more than ordinary interest, something that seemed to
carry his thoughts far away from the scene around him; for when,
presently, he raised his eyes from the book, they looked out straight
before him with a gaze that evidently saw nothing of that on which
they rested.
He was a handsome young fellow of, perhaps, twenty-two years of
age, rather tall, and well-made, with light wavy hair, and blue-grey
eyes that had in them an introspective, somewhat dreamy
expression, but that nevertheless could light up on occasion with an
animated glance.
The house stood on a terrace that commanded a view of the sea,
and, in the distance, white sails could be seen making their way
across the blue water in the light breeze and the dazzling sunlight.
Nearer at hand were waving palms, glowing flowers, humming
insects and gaudily-coloured butterflies—all the beauties of a tropical
garden. On one side of him was the open window of a sitting-room
that, shaded, as it was, by the verandah, looked dark and cool
compared with the glare of the scorching sun outside.
From this room came the sounds of a grand piano and of the
sweet voice of a girl singing a simple and pathetic ballad.
At the moment the song ceased a brisk step was heard coming up
the path through the garden, and a good-looking young fellow of tall
figure and manly air made his way to where the other still sat with

his eyes fixed on vacancy, as one who neither sees nor hears aught
of what is going on about him.
“Ha, Leonard!” the new-comer exclaimed, with a light laugh,
“caught you dreaming again, eh? In another of your reveries?”
The other roused himself with a start, and looked to see who was
his visitor.
“Good-morning, Jack,” he then answered with a slight flush. “Well,
yes—I suppose I must have been dreaming a little, for I did not hear
you coming.”
“Bet I guess what you were dreaming about,” said the one
addressed as Jack. “Roraima, as usual, eh?”
Leonard looked a little conscious.
“Why, yes,” he admitted, smiling. “But,” he continued seriously, “I
have just been reading something that set me thinking. It is about
Roraima, and it is old; that is to say, it is in an old number of a paper
bound up in this book that a friend has lent me. I should like to read
it to you. Shall I?”
“All right; if I may smoke the while. I suppose I may?” And the
speaker, anticipating consent, pulled out a pipe, filled and lighted it,
and then, having seated himself on a chair, crossed one leg over the
other, and added, “Now, then, I am ready. Fire away, old man.”
And Leonard Elwood read the following extract from the book he
had been studying:—
“Will no one explore Roraima, and bring us back the tidings which it has been
waiting these thousands of years to give us? One of the greatest marvels and
mysteries of the earth lies on the outskirt of one of our colonies, and we leave the
mystery unsolved, the marvel uncared for. The description given of it (with a map
and an illustrated sketch) in Mr. Barrington Brown’s ‘Canoe and Camp Life in British
Guiana’ (one of the most fascinating books of travel the present writer has read
for a long time) is a thing to dream of by the hour. A great table of pink and white
and red sandstone, ‘interbedded with red shale,’ rises from a height of five
thousand one hundred feet above the level of the sea, two thousand feet sheer
into the sapphire tropical sky. A forest crowns it; the highest waterfall in the world
—only one, it would seem, out of several—tumbles from its summit, two thousand
feet at one leap, three thousand more on a slope of forty-five degrees to the
bottom of the valley, broad enough to be seen thirty miles away. Only two parties

of civilised explorers have reached the base of the table—Sir Robert Schomburgk
many years ago, and Mr. Brown and a companion in 1869[4]—each at different
spots. Even the length of the mass has not been determined—Mr. Brown says from
eight to twelve miles. And he cannot help speculating whether the remains of a
former creation may not be found at the top. At any rate, there is the forest on its
summit; of what trees is it composed? They cannot well be the same as those at
its base. At a distance of fifteen hundred feet above sea-level the mango-tree of
the West Indies, which produces fruit in abundance below, ceases to bear. The
change in vegetation must be far more decided where the difference is between
five thousand and seven thousand feet. Thus for millenniums this island of
sandstone in the South American continent must have had its own distinct flora.
What may be its fauna? Very few birds probably ascend to a height of two
thousand feet in the air, the vulture tribe excepted. Nearly the whole of its
animated inhabitants are likely to be as distinct as its plants.
“Is it peopled with human beings? Who can tell? Why not? The climate must be
temperate, delicious. There is abundance of water, very probably issuing from
some lake on the summit. Have we here a group of unknown brothers cut off from
all the rest of their kind?
“The summit, Mr. Brown says, is inaccessible except by means of balloons. Well,
that is a question to be settled on the spot, between an engineer and a first-rate
‘Alpine.’ (What is the satisfaction of standing on the ice-ridge of the Matterhorn, or
crossing the lava-wastes of the Vatna-Jökull, compared to what would be the
sensation of reaching that aerial forest and gazing plumb down over the sea of
tropical verdure beneath, within an horizon the limits of which are absolutely
beyond guessing?)
“But put it that a balloon is required, surely it would be worth while for one of
our learned societies to organise a balloon expedition for the purpose. No one can
tell what problems in natural science might not be elucidated by the exploration.
We have here an area of limited extent within which the secular variation of
species, if any, must have gone on undisturbed, with only a limited number of
conceivable exceptions, since at least the very beginning of the present age in the
world’s life. Can there be a fairer field for the testing of those theories which are
occupying men’s minds so much in our days? And if there be human beings on
Roraima, what new data must not their language, their condition, contribute for
the study of philologers, anthropologists, sociologists?
“One more wonder remains to be told. The traveller speaks of two other
mountains in the same district which are of the same description as Roraima—
tables of sand-stone rising up straight into the blue—one larger than (though not
as high as) Roraima itself. It is only because of their existence, and because, for
aught that appears, they may be equally inaccessible with Roraima, that one does
not venture to call Roraima the greatest marvel and mystery of the earth!”

“What is that taken from?” asked Jack Templemore when the
reader had put down the book.
“It is from the Spectator.[5] I say, Jack, what a chance for an
explorer! Fancy people spending their money and risking their lives
in exploring an icy, cold, miserable, desolate region, like the Arctic
Circle, when there is a wondrous land here in the blue skies—yet no
wilderness of ice and snow—waiting to be won; and no one seems
to trouble about it! I do wish you would do as I have so often
suggested—set out with me upon an expedition and let us see
whether we cannot solve the secret of this mysterious mountain.
You have the leisure now, and I have the money. Dr. Lorien and his
son are now on their way back from near there; if they can
undertake the journey, so could we. Besides, it is not as though we
were novices at this kind of travel; we have been on short trips to
the interior times enough.”
Jack Templemore looked dubious. He was, it is true, used to
roughing it in the wild parts of South America. He had been trained
as an engineer, and, for some years—he was now twenty-eight—had
been engaged in surveying or pioneering for new railways in various
places on the Continent. His father having lately died and left him
and his mother very poorly off, he was now somewhat anxiously
looking about for something that would give him permanent
occupation, or the chance of making a little money. He and Leonard
Elwood were great friends; though they were, in many respects, of
very different characters. Elwood was, essentially, of a romantic,
poetic temperament; while Templemore affected always a direct,
practical, matter-of-fact way of looking at things, as became an
engineer. He was dark, tall and sturdily built, with keen, steady grey
eyes, and a straight-forward, good-humoured manner. Both were
used to hunting, shooting, and out-door sports, and, as Elwood had
just said, they had had many short hunting trips into the interior
together. But these had been in previous years, since which, both
had been away from Georgetown. Templemore, as above stated,
had been engaged in railway enterprises, Elwood had gone to
Europe, where, after some time spent in England, during which his

father and mother had both died, he had travelled for a while ‘to see
the world,’ and finally had come out again to Georgetown to look
after some property his father had left him. On arrival he had gone
at first to an hotel, but some old friends of his parents, who lived on
an estate known as ‘Meldona,’ had insisted upon his staying with
them for a while. Here he found that his old friend Jack Templemore
was a frequent visitor, and it was an open secret that Maud
Kingsford, elder of the two daughters of Leonard’s host, was the real
attraction that brought him there so constantly.
Now Jack Templemore, as has been said, was more practical-
minded than Leonard. He had not shrunk from the hardships and
privations of wild forest life when engaged upon railway-engineering
work, when there had been something definite in view—money to be
made, instruction to be gained, or promotion to be hoped for. But he
did not view with enthusiasm the idea of leaving comfortable
surroundings for the discomforts of rough travel, merely for travel’s
sake, or upon what he deemed a sort of wild-goose chase. He had
carefully read up all the information that was obtainable concerning
the mountain Roraima, and had seen no reason to doubt the
conclusions that had been come to by those who ought to know—
that it was inaccessible. Of what use then to spend time, trouble,
money—perhaps health and strength—upon attempting the
impossible?
So Jack Templemore argued, and, be it said, there was the other
reason. Why should he go away and separate himself for an
indefinite period from his only surviving parent and the girl he loved
best in the world, with no better object than a vague idea of
scrambling up a mountain that had been pronounced by practical
men unclimbable?
Thus, when Leonard appealed to him on this particular morning,
merely because he had come across something that had fired his
enthusiasm afresh, Jack did not respond to the proposal with the
cordiality that the other evidently wished for.
“I don’t mind going a short trip with you, old man,” Jack said
presently, “for a little hunting, if you feel restless and are a-

hungering after a spell of wandering—a few days, or a week or two,
if you like—but a long expedition with nothing to go upon, as it
were, seems to me only next door to midsummer madness.”
Leonard turned away with an air of disappointment, and just then
Maud Kingsford, who had been playing and singing inside the room,
stepped out.
Leonard discreetly went into the house and left the two alone, and
Maud greeted Jack with a rosy tell-tale flush that made her pretty
face look still more charming. In appearance she was neither fair nor
dark, her hair and eyebrows being brown and her eyes hazel. She
was an unaffected, good-hearted girl, more thoughtful and serious,
perhaps, than girls of her age usually are—she was twenty, while
Stella, the younger sister, was between eighteen and nineteen—and
had shown her capacity for managing a home by her success in that
line in their own home since her mother’s death a few years before.
The practical-minded Jack, who had duly noted this, saw in it
additional cause for admiration; but, indeed, it was only a natural
outcome of her innate good sense. She now asked what her lover
and Leonard had been talking of.
“The usual thing,” was Jack’s reply. “He’s mad to go upon an
exploring expedition; thinks we could succeed where others have
failed. It’s so unlikely, you know. Now, if he would only look at the
thing practically——”
Maud burst into a merry laugh.
“You do amuse me—you two,” she exclaimed; at which Jack
looked a little disconcerted. “You always insisting so upon being
strictly non-speculative, and Leonard, with his romantic phantasies,
and his dreams and visions, and vague aspirations after castles in
the air. You are always hammering away at him, trying to instil
practical ideas into him with the same praiseworthy perseverance,
though you know that in all these years you have never made the
least little bit of impression upon him. Your ideas and his are like oil
and water, you know. They will never mix, shake them together as
you will.”
“But—don’t you think I am right? Isn’t it common sense?”

“Quite right, of course; and you are persevering; I’ll say that for
you.”
“For the matter of that, so’s Leonard,” said Jack with a good-
natured laugh. “He’s as persevering with this fad of his as any man I
ever met in my life. I do believe he’s got a fixed idea that he has
only to start upon this enterprise, and he will come back a made
man with untold and undreamt-of wealth and——”
“And a princess for a bride—the fair maid of his dreams,” Maud
put in, still laughing. “We have not heard so much of her, by the bye,
lately. He has been rather shy of those things since his return from
Europe, and does not like to be spoken to about them. We began to
think he had grown out of his youthful fancies.”
The fact was, that, from his childhood, Leonard had been
accustomed to strange dreams and fancies. These five—Leonard,
Templemore, and Mr. Kingsford’s son and two daughters—had been
children together, and in those days Leonard had talked freely to his
childish companions of all his imaginative ideas; and as they grew
older, he had not varied much in this respect. Moreover, Leonard had
had an Indian nurse, named Carenna, who had encouraged him in
his fantastic dreamings, and who had, by her Indian folk-lore tales,
early excited his imagination. Her son Matava, too, had been
Leonard’s constant companion almost so long as he could remember,
first in all sorts of boyish games and amusements, and later in his
hunting expeditions; and both Matava and Carenna had been always
more devoted to Leonard than even to his father and mother.
But when Mr. and Mrs. Elwood left the estate they had been
cultivating, to go to England, the two Indians had gone away into
the interior to live at an Indian settlement with their own tribe.
About twice a year, however—or even oftener, if there were occasion
—Matava still came down to the coast upon some little trading
expedition with other Indians; and at such times he never failed to
come to see the Kingsfords and inquire after Leonard.
The Dr. Lorien, of whom mention had been made by Leonard, was
a retired medical practitioner who had turned botanist and orchid-
collector. He had been a ship’s doctor, and in that capacity had

voyaged pretty well all over the world. Since he had given that up he
had travelled further still by land—in the tropical regions in the heart
of Africa, in Siam, the Malay Peninsular and, latterly, in South
America—in search of orchids and other rare floral and botanical
specimens. The vicinity of Roraima being one of the most
remarkable in the world for such things—though so difficult of
access as to be but seldom visited by white men—it is not surprising
that he had lately planned a journey thither.
From this journey the doctor and his son were now daily expected
back. One of the Indians of their party had, indeed, already arrived,
having been despatched in advance, a few days before, to announce
their safe return.
Thus it came about that Templemore and Maud, while still talking,
were not greatly surprised at the sudden appearance of Matava, who
stated that he had come down with the doctor’s party, who would
follow very quickly on his heels.
Maud, who knew the Indian and his mother well, received him
kindly; and, to his great delight, was able to inform him that his
‘young master’—as he always called Leonard Elwood—had returned
to Georgetown, and was at present with them.
Matava had, indeed, expected this, for he had heard of Leonard’s
intention at his last visit to the coast some six months before. He
was greatly pleased to find he was not to be disappointed in his
expectation. Moreover, the Indian declared, he had news for him
—“news of the greatest importance”—and begged to be allowed to
see him at once. So Maud sent him into the house—where he knew
his way about perfectly—to find Leonard; and then, turning to
Templemore, she said, laughing,
“I wonder what his ‘important’ intelligence can be? Some deeper
secret than usual that his old nurse has to tell him, I suppose.”
“I hope it’s nothing likely to rouse a further desire to set off on
this mad-cap expedition he has so long had in his mind,”
Templemore returned; “for,” looking at her with a sigh, “if he should
make up his mind to start, I am, in effect, pledged to go too,
whether I wish or not.”

“Why should you expect it? and how are you obliged to go?” Maud
inquired with evident uneasiness.
“I know that Leonard saw Dr. Lorien in London before he came out
last, and had a long talk with him. When he learned of the
expedition upon which the doctor was then setting out, he was
much annoyed at being unable to join him. He said, however, that
he should be in Georgetown himself in a few months, and hoped to
see the doctor on his return; and he particularly asked him to try to
collect for him all the information and particulars he could
concerning the best route by which to make the journey to Roraima.
Dr. Lorien told me all this before he left us, adding that he felt
certain Leonard’s object in coming again to Georgetown was quite as
much to arrange for an expedition as his ostensible one of looking
after his property. And I know, too, from what I have seen since
Leonard has been back, that his thoughts are full of the idea. You
say he does not now talk much of it to you or to others?”
“No; and as I told you just now, we had begun rather to think he
had given up his former romantic yearnings for adventure; and,
when you have referred to them before him, I have thought that you
were only teasing him a little about old times.”
“Oh dear no; by no means. Whatever he may say, or leave unsaid
to you and his general acquaintances, he is, in his heart, just as
much set upon it as ever.”
“It is odd, that,” Maud observed thoughtfully, “because he used to
be so fond of telling us about his dreams and visions and all the
castles in the air and half-mystical imaginings he used to build upon
them. But,” she went on slowly, “I have noticed that, since his long
absence from us, Leonard Elwood is very different from what he was
as I remember him. He seems, at times, so reserved and distant, I
almost feel inclined to call him ‘Mr. Elwood’ instead of ‘Leonard.’ And
he is, in a manner, unsociable, too. He is so preoccupied always, so
silent, and so wrapped up in himself, that you generally have to wait,
if you speak to him, while he collects his thoughts—brings them
back from the distant skies or wherever they have gone a-wandering
—before he replies to you. Not that he is intentionally cool or

distant, I think; and I am sure he is just as good-hearted as ever. Yet
there is a change of some sort. Stella says the same. And, do you
know, he sometimes gives me a sort of feeling as though he were
not English at all, but of some other race, and that he feels half out-
of-place amongst us, a fish out of water, as it were? I wonder
whether he is in love!” And Maud gave a ringing little laugh.
Templemore shook his head.
“If he were, it would be with some young lady on the other side of
the Atlantic,” he returned. “And he would not be desirous of
prolonging his stay on this side. No; I know what is the matter with
him. He talks freely enough to me. And, now that he is expecting Dr.
Lorien back, he is gradually working himself up into a state of
excitement and expectation. He has quite made up his mind for
some news or information—Heaven only knows why—and that is
what makes him by turns restless and preoccupied. If, therefore,
what Matava has to tell has anything to do with what I know to be
so much in his thoughts, it may be the means of deciding him to go;
and then I should have to go too.”
“But why? I don’t see what it has to do with you, Jack.”
“It has this to do with me, dear Maud,” said Templemore, taking
her hand; “Leonard, some time ago, made me a very handsome—to
me a very tempting—offer if I would make up my mind to start with
him on this vague expedition. He offered me £300 clear, he paying
all expenses, and giving me, besides, half of whatever came out of
it. Unfortunately for myself, I am not now in a position to say ‘no’ to
such an offer. I have been, now, nearly a year waiting for something
to ‘turn up.’ My mother has barely enough to live on, and depends
upon me for ordinary comforts, to say nothing of little luxuries; and
what I had saved up from former engagements is steadily getting
less and less, and will shortly disappear. I do wish with all my heart I
could get anything else, almost, rather than this wild-goose affair of
Leonard’s. Yet nothing has offered itself; so what am I to do? For
your sake, for the hope of being able one day to provide a home for
you——”

“Nay, Jack,” Maud interposed, with a deep flush, “do not say for
my sake. I would not have you set out on an enterprise of danger
and difficulty for my sake. But I see clearly enough you must do it, if
it be again offered, for your mother’s sake. Yes, for hers, you must.”
The girl hesitated, and it was easy to see she found it hard to say
the words, but she went on bravely, “So, I repeat, if it be again
offered, you must accept it, Jack. And be sure I will look after your
mother, and comfort her while you are away.”
“That is spoken like my own dear girl,” Templemore answered with
emotion. “Yes, I cannot well refuse; and I know I may look to you to
console my mother. You will comfort each other.”
Just then they heard Leonard’s voice calling out in excited tones
for Templemore. A moment or two later he came rushing out of the
house.
“Jack, Jack!” he cried. “Such a strange thing! Here is our
opportunity! Matava has brought some extraordinary news!”
Leonard was so incoherent in his excitement, that it was some
time before his hearers grasped his meaning.
His news amounted, in effect, to this. A white man had been
staying for some time near the Indian village at which Carenna and
her son Matava lived; and he had had many talks with both about a
project for ascending the mountain of Roraima. It being an arduous
undertaking, he sought the co-operation of one or two other white
men; and Leonard’s old nurse had urged him to communicate with
her young master, who would shortly be in Georgetown, assuring
him that he would be the very one—from the interest and
enthusiasm he would feel—to join him and help him to achieve
success if success were possible. Matava, who knew of Dr. Lorien’s
presence in the district, had suggested to the stranger to go to see
him, and a meeting had thus been brought about. The doctor would
tell him the result; but the main thing was that the stranger had sent
an invitation to Leonard to join him and to bring, if he pleased, one
other white man, but no more. The doctor was now at the
Settlement, near the mouth of the Essequibo, transferring to the
steamer, from the Indian canoes in which they had been brought

down the river, his botanical treasures and other trophies of his
journey. If Leonard wished to go back with the canoes and the
Indians who were with them, he would have to let them know at
once, and they would wait. Otherwise they would be on their way
back in a day or two; which would involve the organising of a fresh
expedition—a matter of great trouble—should Leonard make up his
mind to proceed later.
The enthusiastic Leonard needed no time to make up his mind.
“I shall go,” said he. “If you will come too, Jack, I shall be only too
glad. But, if not, I may be able to find some one else; or I shall go
alone. So I shall send word at once to keep the boats and the
Indians.”
“But,” objected Maud Kingsford, “consider! You know nothing of
this stranger; he may be a blackleg, an escaped murderer or
desperado, or all sorts of things.”
“No, no! Carenna knows. She has sent word that I can trust this
man, and she knows. She is too fond of me to let me get mixed up
with any doubtful character. Dr. Lorien, too, and Harry have seen
him, and talked with him, and think well of him; so Matava says. I
shall know more when I see them in a day or two. Meantime, I shall
keep the canoes and Indians, and risk it.”
Then he rushed off to have a further talk with Matava, and, as he
said, see about getting the Indian “some grub.”
Jack and Maud, left alone, looked at each other in dismay. It had
been one thing to talk vaguely of what they would do in case
Leonard should take what at the time seemed a very unlikely step. It
was quite another to be thus suddenly brought face to face with it.
Maud turned very pale and seemed about to faint. She felt keenly
how hard it would be to see her lover depart upon an adventure of
this uncertain character, the end or duration of which no one could
even guess at. But she recovered her self-possession with an effort
and, looking steadily at Templemore, said,
“What you said you would do for our sakes is to be very quickly
put to the test, it seems. You—will—go, Jack?”
“Yes,” he answered firmly; “since it is your wish.”

“You must,” she answered. “It is hard to lose you; it will be hard
for us both. But go—and go with a good heart. Be sure I will be a
daughter to your mother while you are away.”
He took her hand in his and pressed it to his lips.
“For your sake, dear Maud, I shall go,” he said. “For your sake and
for my mother’s; in the hope that some success may result; but not
—Heaven knows—for the mere sordid hope of gain.”
[3] The Indians of British Guiana pronounce this word Roreema.
[4] Since then Roraima has been visited by two or three other
travellers; but their accounts have added little to our knowledge.
They entirely confirm Mr. Brown’s statements as to its
inaccessibility. (See Preface.)
[5] This article appeared in the Spectator of April 1877.

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Repetitive project scheduling theory and methods 1st Edition Zhang

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