Hot springs are numerous in all parts of the world. The water of most hot springs has decided mineral properties, for the reason that hot water passing through mineral strata will dissolve more of the mineral substance than cold water. Many hot springs are great resorts for invalids because of their curative properties. The famous Silver Spring in Florida has the dimensions of a small lake, and boats sail over it, and a small river continually flows from it. The inhabitants of Chaudes Aigues, France, use the water of the hot springs to cook their food, to wash their clothes, and warm their houses. The heat from these springs is worth about $30 per day, as it is equal to the heat produced by five tons of coal. Few things in nature are more beautiful and impressive than a river bursting from the hillside, its clear water sparkling in the sunlight, seeming joyous at being free from its captivity. Among the most celebrated and beautiful of subterranean rivers is the Sorgues of Dauclûse, in France. It flows for miles through a cave, and discharges thirty cubic yards per second. Soon after it issues from the cave it divides into numerous irrigating channels, and spreads fertility over an area of more than eighty square miles. Echo River in Mammoth Cave is navigated by boats for nearly a mile, and in some places is two hundred feet wide. The Poik River in Austria flows through the famous cave of Planina. The cave can only be explored by a boat. Professor Schmidt, with three companions, navigated the river for more than a mile. Along the continental shores many outlets of subterranean rivers may be seen. In 1857 all that part of the sea adjacent to the southern point of Florida received an immense eruption of fresh water. Intelligent observers estimated that for more than a month this remarkable inundation of a subterranean river discharged as much water as the Mississippi, and spread all over the strait, thirty-one miles wide, that separates Key West from the mainland of Florida.