regulated by the temperature of the strata through which the water percolates. The geysers of Iceland send up enormous jets of hot water in the midst of Arctic cold. [Illustration: OLD FAITHFUL GEYSER. (Yellowstone National Park). PHOTOGRAPH BY F. J. HAYNES, ST. PAUL.] The earth is nature’s great filter, cleansing and purifying the water from the impurities of the soil. As it passes through strata of gravel or clay, it becomes pure and wholesome to drink. Sometimes water passes through a stratum containing sulphur, iron or magnesia, and so we have mineral wells and springs. There is in Brown County, Illinois, an iron, a sulphur, and a magnesia spring within a few feet of each other. Having considered underground streams and lakes, artesian wells, and geysers in a general way, we will now proceed to notice some of the most remarkable of each. Of underground lakes we know but little. We cannot enter them as we do a cave, and if we could now and then find an entrance to them, we should find little room between their surface and the strata above it for navigation. We infer their existence, because they are necessary to supply many underground rivers and smaller streams that come to the surface and discharge their waters into the ocean. Another proof of their existence is found in the large areas of country where deep water is struck at a uniform depth measuring from the ocean level. The bogs of Ireland are floating upon underground lakes. Springs are gems of the first water, as the dealer in precious stones would say of a perfect diamond. They do not impress us with their size so much as the way they minister to our comfort. But few wells equal them in the variety and purity of their waters. I remember a spring back in New England, which burst forth from a bed of gravel at the side of a hill with such force that it seemed to fairly boil, though icy cold and clear as crystal. So violent was the ebullition that the gravel and pebbles were continually thrown to the surface. Then it ran leaping, gurgling and sparkling down a steep declivity, and was joined on the way by rivulets from three smaller springs, so that when it reached the level of the valley it became a quiet, well-behaved brook, the home of the speckled trout. In places where it spread out over a gravelly bed the birds would light upon the stones and sip the water, and fly away singing joyous notes for so exquisite a luxury. A half mile from its source this brook became quite broad and deep. It ran through a pasture, and cattle came and slaked their thirst.