The ocean itself is known to possess springs, copious ones, in many places the fresh water rising up through the heavier salt as through a rock, and affording supplies to vessels at the surface. Off the coast of Florida many of these submarine springs have been discovered, the outlet, probably, of the streams and rivers that disappear in the "sinks" of that State. It is a pleasant conception, that of the unscientific folk, that the springs are fed directly by the sea, or that the earth is full of veins or arteries that connect with the great reservoir of waters. But when science turns the conception over and makes the connection in the air,--disclosing the great water-main in the clouds, and that the mighty engine of the hydraulic system of nature is the sun,--the fact becomes even more poetical, does it not? This is one of the many cases where science, instead of curtailing the imagination, makes new and large demands upon it. The hills are great sponges that do not and cannot hold the water that is precipitated upon them, but let it filter through at the bottom. This is the way the sea has robbed the earth of its various salts, its potash, its lime, its magnesia, and many other mineral elements. It is found that the oldest upheavals, those sections of the country that have been longest exposed to the leeching and washing of the rains, are poorest in those substances that go to the making of the osseous framework of man and of the animals. Wheat does not grow well there, and the men born and reared there are apt to have brittle bones. An important part of those men went downstream ages before they were born. The water of such sections is now soft and free from mineral substances, but not more wholesome on that account. The gigantic springs of the country that have not been caught in any of the great natural basins are mostly confined to the limestone region of the Middle and Southern States,--the valley of Virginia and its continuation and deflections into Kentucky, Tennessee, northern Alabama, Georgia, and Florida. Through this belt are found the great caves and the subterranean rivers. The waters have here worked like enormous moles, and have honeycombed the foundations of the earth. They have great highways beneath the hills. Water charged with carbonic acid gas has a very sharp tooth and a powerful digestion, and no limestone rock can long resist it. Sherman's soldiers tell of a monster spring in northern Alabama,--a river leaping full-grown from the bosom of the earth; and of another at the bottom of a large, deep pit in the rocks, that continues its way under ground.