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Show 26 GEOLOGY OF THE HIGH PLATEAUS. really taken place, how they are related to each other, what dislocations have been produced by them, and what are the present and what were probably the former attitudes of the disturbed masses ; and yet there are very few subjects in the range of geology so difficult to study. It seems as if Nature were ashamed of her scars, and resorted to numberless tricks and devices to hide them from sight; here smoothing over the break and deftly hiding it with a mantle of soil; there confusing the inquisitive student by a multiplicity of perplexing forms, which are sure to worry if not to mislead him; and always shy of the truth. Throughout the greater part of the Plateau Province, Nature is so poorly clad in the raiment of soil and vegetation and the earth is so well dissected by erosion that these features do not easily escape the scrutiny of the determined and experienced investigator. In the High Plateaus, however, the faults are less readily scrutinized than in some other parts of the province, though much more conspicuously displayed than in smoother and moister countries or than in countries of more complicated structure. While I suspect that many minor faults have escaped detection, I am confident that all of the grander ones have been discovered and their principal features and relations unraveled. All of the greater displacements of the district present certain well-marked habitudes. Most important among them is the strict homology of the faults with monoclinal flexures. In truth, so close is the homology, that we are justified in calling a monoclinal in some of its aspects a modified fault. The only difference for structural purposes is that in the case of a typical~fault of the simplest form the shearing is along one plane, while in the monoclinal the shearing lies between two planes. We have also cumulative or repetitive or " step-faults," where the shearing is subdivided among several planes. All have this in common, that the passage from the uplifted to the lowest thrown side is through a very narrow zone, which has its width reduced to zero in the case of the single or simple fault. All of the great lines of displacement assume all of these modifications in different parts of their extent. In one place the fault is simple. A few miles farther along its course it may become subdivided into a series of "step-faults;" still farther on, into a perfect unbroken monoclinal; it may be at another locality a faulted monoclinalâ€"a part of the displacement being through flexing and |
