There are three great rock-making processes, namely: sedimentation movements of the melted rock or rock magma from within outwards metamorphism, or transformation of rocks by heat, pressure, and the influence of hot liquids and gases. These will now be discussed in order; and after the description of each process, there follows an account of the … Read more

Three Classes of Rocks.—The rocks are divided into three great classes: Sedimentary rocks, made of fragments of older rocks more or less water worn or ground to powder, and then spread out and deposited in layers of gravel, sand, mud, etc., to be later consolidated by pressure and natural cementing. The material may also consist … Read more

Weathering Forces Under this head are grouped a number of agencies that have their origin in the atmosphere, and which work not only on the surface but as far down as air and water, heat and cold, can penetrate. Because these forces work invisibly, they are apt to be more or less overlooked, although the … Read more

Origin of Glaciers In temperate and cold climates, and even in tropical countries, where there are very high mountains, the wastage of the snow by melting and evaporation may be less than the snowfall on the tops of the mountains; the snow, therefore, accumulates continually. In cold climates, like that of Greenland, snow accumulates even at … Read more

Forces Causing Erosion It is plain that ever since the crust of the earth became stable enough to allow water to stand, waves to form, rain to fall, and weather to act, these forces have been working on the surface much as they are doing now. It is quite possible that in earlier ages they … Read more