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Show Viii GEOLOGY OF THE HIGH PLATEAUS. teau Province. In general, each formation is exceedingly persistent and homogeneous in its characteristics, but in passing from one formation to another in the vertical scale great heterogeneity is observed. To a very large extent the formations still lie in a horizontal or nearly horizontal position. The entire surface is traversed by faults or their homologues, monoclinal flexures, having in general a north and south direction. Following any given line of displacement frequent transitions from faulting to flexure are observed. The method of transition is variable; sometimes the flexed beds are found to be partially faulted so that the throw is part by faulting and part by flexure; sometimes a great fault divides into two or more minor ones in such a manner that the entire throw is accomplished by a series of steps. Still other important phenomena are observed in these faults; to explain them, the terms throw and upheaval are used as relative to each other. In the cases to be described the upheaved beds have their edges flexed upwards. This is explained in the following manner : First, a displacement occurred by flexure; second, another displacement, reversing the first, occurred by faulting, so that the thrown beds of the first displacement were the upheaved beds of the second. The evidence of this reversed action is sometimes exhibited in beds deposited at a time intervening between the two movements; in this manner the beds last deposited are displaced only by the last movement. This reversal of displacement along the same plain or zone is frequently seen. It is sometimes by faulting and sometimes by flexure, thus giving rise to many complications in the positions of strata. The great displacements began in early Tertiary time, and are probably yet in progress. The evidences of the recency of some of these movements appear in the escarpments frequently seen along the line of faults where Quaternary beds have been broken at a time so recent that the escarpments have not been destroyed by atmospheric agencies, and further evidence is exhibited in the small amount of talus frequently found at the foot of a recently formed fault-scarp. By these displacements the region is divided into blocks with a north and south trend; but this geologic characteristic serves only in part to divide the region into plateaus. The streams which traverse the region have their sources in the Wind |