DIFFERENT EPOCHS OF DISPLACEMENT. 43 



eruptive district seem to have had portions of their shearing before the 

 beginning of the principal epoch of displacement. But these earlier symp- 

 toms are usually like old wounds which had once healed and afterwards 

 broke out again with increased disorder. The Sevier fault, in particular, 

 shows signs of two epochs of activity in some portions of its extent. Be- 

 tween Monroe and Gunnison it appears as a fault cutting along the axis of 

 a small but sharp monoclinal flexure. The flexure is clearly older than 

 the fault. The Musinia faults cut obliquely across the great monoclinal of 

 the Wasatch Plateau, and show little sympathy with it. The Paunsagunt 

 fault, uniting with the northern extension of the East Kaibab flexure, is 

 plainly independent of it, and is decidedly younger. It is a most curious 

 circumstance that where we find this two-period displacement the motion 

 of the fault is often reversed — the lift of the first period is the throw of 

 the second. It is not always so, but I believe it to be true in a majority 

 of cases where the double movement has been detected. On the other 

 hand, where the shearing of both periods has been in the same direction, 

 the movements would be much more difficult to separate, and many such 

 double movements doubtless have escaped observation. 



All of the displacements thus far discussed belong to the same system. 

 Whether older or younger, they lie along the same lines and very seldom 

 show any interferences. None of them will go back of the Pliocene in age, 

 and I think it probable that none of them will go behind the middle Plio- 

 cene. Older displacements along these lines, if they exist, are wholly cov- 

 ered up and obliterated, and cannot be separated at present from the later 

 ones of this system. 



There is, however, a totally distinct system of displacements, belong- 

 ing to a much earlier age, which the grander and more general erosion of 

 the country has brought to light, but which can never be confounded with 

 the Pliocene-Quaternary system. They make a wide angle with the lat- 

 ter series and have a history wholly independent of them. They are only 

 occasionally revealed in a fragmentary manner in places where deep gorges 

 have cut through thousands of feet of Tertiary formations and volcanic 

 emanations, or where erosion has swept off corresponding amounts of strata 

 from broad districts. Only in two or three places in the heart of the High 



