RELATION OF FAULTS TO ANCIENT SHORE LINES. 45 



time and possibly are Pre-Tertiaiy. Mr. Gilbert has studied the Water- 

 Pocket flexure, and believes that its epoch belongs to the interval which 

 separates Tertiary from Cretaceous time. The Echo Cliff flexure is proba- 

 bly much younger. The San Rafael flexure remains to be studied. None 

 of them appear as yet to have any sympathy with the Pliocene-Quaternary 

 faults of the High Plateaus. 



It yet remains to speak of another interesting relation of the later 

 system of faults. They have throughout preserved a remarkable and per- 

 sistent parallelism to the old shore line of the Eocene lake, following the 

 broader features of its trend in a striking manner. The cause of this rela- 

 tion is to me quite inexplicable, so much so, that I am utterly at a loss to 

 think of any subsidiary facts which may be mentioned in connection with 

 it and which can throw light upon it. It seems best, therefore, to allow 

 the main fact to stand by itself, and not to confuse it with any others with 

 which it has no certain relation. 



The faulting and flexing has been associated with a general increase in 

 the altitude not only of the district of the High Plateaus, but of the country 

 south and east of them. The uplifting has by no means been confined to 

 the few tabular masses. Wherever we look in the western part of the Pla- 

 teau Province the signs of this elevation are unmistakable. In some local- 

 ities it was much greater than in others, but the signs of it are common to 

 all. It is betrayed in the drainage channels. At a comparatively recent 

 epoch there has been a sudden renewal of activity on the part of the 

 streams, by which they have taken to canon-cutting with renewed energy 

 as if their slopes had been increased, and this is especially observable in 

 the Colorado itself, where the effect has been a maximum. The tribu- 

 taries have responded and have acted in like manner. Just prior to the 

 advent of this regional uplifting, the aspect of the region appears to 

 have been that which would naturally have resulted from a long period 

 of stability at the same altitude. The canons and intervales were wide, 

 and long stretches of the rivers were at or near their base-levels, having 

 eroded as deeply as possible, then slowly widened their valleys and made 

 flood-plains. All at once a new era of canon-cutting set in, and profound 

 narrow chasms were sawed in the strata and are to-day sinking deeper. 



