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. Fol- 

 lowing 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 man- 

 ner : First, a displacement occurred by flexure ; second, another displace- 

 ment, reversing the first, occurred by faulting, so that the thrown beds of 

 the first displacement were the upheaved beds of the second. The evi- 

 dence 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 some- 

 times by faulting and sometimes by flexure, thus giving rise to many com- 

 plications 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 fre- 

 quently 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 



