6. The points of resemblance between the two sections exposed, one by a steam shovel, the other by river action, are the horizontal position of the strata and the alternations of beds of unlike character. The differences are mainly that the beds making up the mountain show that they are built up of alternating layers of sand (now converted into a sandstone) and clay (now in the condition of a slate). Are not these the products of a decayed continent? Is their position to be explained otherwise than along the lines already stated? Our only difficulty in readily accepting this conclusion is founded on a hereditary belief, born in ignorance and nourished to maturity by superstition, that the earth came into existence as we see it to-day, the surface dissected by valleys in which the rivers find established courses to the sea; possessing a multiplicity of highland and lowland, granite mountains and marble hills, as a result of some plan carried into effect as a creative act. Science has revealed the impossibility of this interpretation. Considered in the light of evolution, acting through an immense period of time, by means of the processes already enumerated, the diversity of land form is made plain to us, and the ever-varying characters of rock structure and composition are in the main made easy of comprehension. Viewed in the light of the foregoing pages, and illustrating as they do land form and the greater part of the earth's crust, the rock structures revealed on the sides of the mountains and canons, as well as the broader valley itself, take on a new and more intelligent interest. High and enduring as the mountains may appear, resistant as their solid rocks may seem, they are doomed as mountains to the same fate that their own structure and composition-prove to have overtaken earlier mountains before them.
The earth has known no cessation in this cycle of decay, deposition, and elevation; again and again have continental masses been raised from the ocean floor only to become a prey to the forces that destroy them. These cycles will continue—mountain ranges will fade away and new ones will be born. A more permanent relationship between the lowland, the upland, and the ocean level will never be attained until the forces that warp and wrinkle the earth's crust shall have ceased forever.