Surprise has been manifested and inquiries have been made as to the cause of mountains, but the cause which produced the valleys or depressions of the earth is just as much a matter of wonder. Some suppose—indeed, it is a very general opinion—that all the lower parts of the earth's surface are covered with water, but this is not exactly so. Seas, lakes and rivers are only lower than surrounding lands, but there are many inhabited portions of our globe which are much lower than some great seas and lakes. Thus the waters of Lake Erie are about tw5 ^hundred feet higher than the rich cultivated plains surrounding Lake Ontario, but the latter lake is some feet lower than these plains, and is the receptacle of their drainage waters. The most extensive and wonderful depression of the earth is in Asia. It is a vast region of about 18,000. leagues square; it is occupied, to be sure, mostly by the Caspian Sea, but it also contains populous cities and extensive cultivated districts situated in a depression of three hundred and twenty feet below the level of the Black Sea. It is an opinion pretty generally admitted by scientific men at the present day, that the mountains have been formed by the upheaving of their materials, and that they have issued from the bosom of the earth. The necessary consequence of a vast upheaval would be the depression of another portion of the earth. Asia abounds in lofty mountains, and the vast depression of the Caspian Sea and its adjacent plains is surrounded with great mountain chains, hence it is supposed that the elevation of these masses caused a consequent depression of the Caspian valleys.