138 FRANCIS PARKER SHEPARD 



uplift of the Pur cell Range, these streams maintained their courses 

 and developed antecedent drainage. That the old Purcell Range 

 existed on both sides of the trench in this zone is evidenced by 

 finding the typical Purcell strike on the east as well as on the west 

 side of the trench. Also the Purcell series (pre-Cambrian) is 

 present on both sides of the trench in this zone.^ 



The great width of this portion of the valley, 16 miles, is out of 

 accord with the rest of the trench, which might be explained by 

 greater age. Also there was found a continuation of the antecedent 

 portion of the trench up into the Purcells leaving the trench in the 

 vicinity of Cranbrook, and it is just south of here that the trench 

 is found to be again connected with structure. 



3. The southern part. — The southern structural unit extends 

 from Bull River down to Gateway, In this zone there is a thrust 

 fault on the east side of the trench which causes the Mississippian, 

 or in some cases the Devonian, to be brought into contact with the 

 Galton series, partly Cambrian and partly pre-Cambrian,* on the 

 east. Large disconformities in this general region make it difficult 

 to estimate the displacement of the fault. It probably is not more 

 than 2,000 or 3,000 feet north of Elko, but at the boundary Une it 

 was estimated by Daly^ to be as much as 10,000 feet. Ten miles 

 south of Bull River it virtually dies out. Here the Devonian Hme- 

 stone comes down from the mountains into contact with the 

 Mississippian in the valley. 



This fault, which appears to Hmit the east side of the trench 

 from Bull River to Gateway, was considered to be a normal fault 

 by both Daly* and Schofield.^ The writer has no definite proof that 

 this is not the case, but there are several facts which suggest that 

 it is a thrust fault. In the first place the trace of the fault plane at 

 Gateway was followed with considerable certainty for several miles, 

 and it was found that the fault plane curved decidedly up a tribu- 

 tary valley to the east (Fig. 7) . This, of course, suggests an east- 



^ S. J. Schofield, "The Origin of the Rocky Mountain Trench," Trans. Roy. Soc, 

 Can. (1920). P. 76. 



* S. J. Schofield, Science, Vol. LIV, p. 666. 



3 R. A. Daly, Geol. Surv. Can. Mem. 38, p. 118. 



4 Ibid. 



5 S. J. Schofield, "The Origin of the Rocky Mountain Trench," Trans. Roy. Soc. 

 Can. (1920), p. 76. 



