The variable distribution of heat has produced a striking effect in modifying the earth's surface. The cold of the polar regions covers them at all seasons with an extensive deposite of snow and ice, the margins of which are periodically dissolved by the increasing warmth of summer, to be repaired during the succeeding winter. The numberless icebergs, originally formed on the land or in its vicinity, floating on the ocean, and drifted by winds and currents, often pass into more genial regions, producing occasional variations of temperature. The elevated ridges of mountains experience a similar degree of cold, and in all climates, even in the torrid zone, are covered towards their summits with perennial snow. Limited as are our powers of examining the interior of the globe, we yet find in its crust indications of a power which, by operating so as to produce apparent confusion, has effected results highly beneficial to the beings by whom the earth has been peopled. The strata, at first regularly superimposed upon each other, and consisting of those diversified materials which are supplied by the disintegration of pre-existing rocks, have been broken up, and inclined in every possible degree, so as to form those depressions and elevations which we every where observe on the surface. These inequalities have been increased by the protrusion of masses from the more central regions, and the whole has been subjected to the agency of powerful currents of water, by means of which the angular cavities and projections have been smoothed or filled up. The consideration of these phenomena constitutes a distinct branch of natural science. The mountains, rocks, and strata, are composed of ingredients which in themselves are worthy of examination, and capable of affording intense interest. The extremely-diversified forms which these substances assume, their various properties, their uses in the economy of nature, and the purposes to which they may be applied by man, render their investigation not less useful than pleasant.