The document discusses tension springs, which are natural springs that form when certain geological conditions are present underground. Specifically, there must be a sloped layer of porous rock called an aquifer that allows water to flow through it. There also must be layers above and below the aquifer made of non-porous rock or clay called aquicludes that block the flow of water and prevent it from draining out of the aquifer. When it rains, water enters the aquifer and collects at the low end, creating pressure. If there are cracks in the rock running from the aquifer to the surface, the pressure can force the water up through the cracks, causing it to constantly flow out of tension springs located on the land above