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Show ALLUVIAL OB TORRENTIAL CONGLOMERATES. 219 is a process which has often awakened the surprise of engineers who are called for the first time to deal with the problems of harbor protection and is ever revealing wonderful things. Not only does the finer loose material move in grand procession under the influence of unseen, though still comprehensible, agencies, but very coarse detritus is carried slowly with it. The tendency of the process, however, is not towards an indiscriminate mixing of all sorts and sizes, but towards the grouping into layers, here of coarser, there of finer, stuff, according to the variations in the power of the moving water. But there is another class of conglomerates which claims our special attention. These are of alluvial origin, formed, not beneath the surface of the sea nor of lakes, but on the land itself. They do not seem to have received from investigators all the attention and study which they merit. They are usually called gravelsâ€"perhaps are sometimes or even frequently mistaken for glacial driftâ€"but their homology to the ordinary stratified conglomerates of the systematic strata is not always recognized. Throughout great portions of the Rocky Mountain region they are accumulating to-day upon a grand scale and have accumulated very extensively in the past. The processes of degradation are far more energetic and effective in mountains than upon plains. The agents which disintegrate rocksâ€"frost, rain, chemical solutionâ€"have the greatest freedom of action upon the steep slopes of the numberless ravines, and are continuously breaking off fragments and reducing them to sand, gravel, and clay. Not only is the greater part of the finer mold gathered up by the swift rills and torrents, but fragments of considerable size, attaining, under favorable circumstances, the weight of several tons, are caught and urged downward in rushing rapids with an energy which must be seen in order to be realized. The many • streamlets and filaments of a mountain amphitheater gradually unite, as we descend from the crest of the mountains, generating a creek, which attains its greatest flood near the mountain base, and when the snows melt in the spring its swollen current sweeps onward a mass of clastic material of every description from impalpable clay to bowlders. Within the mountain masses the descents are rapid and the streams are torrents. Reaching the valleys |