In the preceding brief description of the Solar system, we see distinctly the relation which our own Earth bears to the other planets, in its position, its form, its magnitude, its satellite, and its daily and annual motions. But though a comparison of these properties of the earth, which constitute what may be called its astronomical condition, with the analogous properties of the other planets, might entitle us to ascribe to them other functions,—the function, for example, of supporting inhabitants, which the earth only is known to possess, yet our argument will derive new strength, and we shall be prepared to meet recent objections, by taking into consideration the geological structure of the earth, and the properties of its atmosphere, and by endeavouring to read its past history in the successive steps by which it has been prepared as a residence for the human family.

The earth, as we have seen, when merely examined by the eye, consists of land and water. The land is composed of soils of various kinds, and of stones and rocks of different characters. It is formed into extensive plains, into valleys excavated apparently by rivers or water-courses, and into mountain groups and mountain ranges, rising to the height of several miles above the bed of the ocean.