Following the order of our topic, let us see what we can find out about underground streams and lakes, and why we know they exist when we seldom see them. We know that large rivers after flowing miles upon the surface of the earth suddenly drop into subterranean channels and reappear after running miles underground. Springs which are always flowing must be constantly fed from some source beneath the surface of the earth. In boring wells the augers, after going down to various depths, suddenly drop several feet, showing that they have reached a cavity in the earth or a fountain of water; if the water gushes up it is evident a fountain has been struck. Where does the water come from to fill the underground lakes and reservoirs and keep the rivers constantly flowing? Geologists tell us that all the land surface of the earth was for vast ages under water; that the great oceans that now roll between the continents once covered them entirely, but after long ages mighty internal forces of the earth raised them above the ocean’s level. For a long time after the hills and mountains were raised above the surface of the ocean, where the valleys and prairies now are there were lakes and inland seas. The water in these lakes and seas did not all evaporate or find its way to the ocean by the rivers that flowed from them. Deep down into the earth much of it found its way, along the fissures and porous strata, until it reached some impervious stratum, as clay or granite. But as this first underground supply would in time become exhausted, by flowing into the ocean through the rivers they fed, nature has made further provision for keeping up the supply. Everywhere upon the surface of the earth where there is water or moisture evaporation is going on. The sun raises enormous quantities of water in the form of vapor, which forms clouds and descends in rain. A part of this water is soon restored to the sea by the rivers, but by far the largest portion penetrates the earth’s surface, as water would penetrate cloth or a sponge when poured upon it. Rain penetrating the earth goes down until it comes to some substance that it cannot penetrate. Then, in trying to find its level, it will distribute itself just as it does upon the surface of the earth. It will find its way into cavities, large and small, or following some underground channel or stratum, it may burst forth a clear and sparkling spring, or it may flow on a rivulet, or river, and perhaps enter into a great subterranean lake. The underground fountain or lake that keeps an artesian well spouting from year to year may be fed by a stream or lake in the heart of some distant mountain. Some artesian wells cease to flow after a while, showing that the fountain that supplies them is at least partially exhausted. We do not know to what depth water penetrates the earth. Artesian wells have been bored in recent years to the depth of four thousand feet. The temperature of springs and artesian wells is