OVERTHRUST TYPE OF FAULT. 387 



is expressed chiefly in the widening of the exposure of the Mormon sand- 

 stone. 



The evidences of faulting observed in the different parts of mount 

 Jura are not to be considered as indicating so many faults, but rather 

 different portions of one great fault* If we join together all the sur- 

 faces along winch faulting has taken place to form one continuous sur- 

 face, it is evident that such a surface must be greatly warped. Its posi- 

 tion on the western slope of mount Jura is quite clearly indicated by 

 the exposures already noted. It first appears at an altitude of 5,100 

 feet in the one case, and 4,550 feet in the other. At both places the 

 fault has a gentler dip southwestward than the slope on which it occurs, 

 so that the fault surface at the points indicated leaves mount Jura in the 

 direction of the lower slope of mount Grizzly. Above these points the 

 fault surface is nearly parallel with the slope, but just below the siliceous 

 eruptive it plunges deep into mount Jura with an easterly dip, along 

 which the three formations of the western slope of the mountain are 

 repeated in the same order on the opposite side. 



It has been remarked that the throw of the fault in the northern por- 

 tion of mount Jura is snyill, hut in the southern portion of the moun- 

 tain it is about three-fourths of a mile. The southeastern portion of 

 the mountain, which is made up of the whole Jurassic series, has been 

 shoved far to the eastward, so that the Hinchman tuff laps much further 

 over upon the Foreman slides in that vicinity than further northward. 

 Their easterly extension connects directly with the faulting, and we may 

 consider that the fault, after passing through mount Jura with an easterly 

 dip. rises to the surface again with westerly inclination between the 

 Hinchman tuff and the Foreman slates, as shown in the section. 



The fault on which the upper and eastern portion of mount Jura has 

 been displaced is thus shown to he an irregularly curved or undulating 

 surface, the general position of which is nearly horizontal, with a low in- 

 clination to the southwestward, and the average hade of the fault is 

 toward the upthrow. It ia evident also that the overturning of tin; 

 Jurassic strata has been from the southwest toward the northeast, ami 

 thai the faulting, which is in the same direction, has taken place subse- 

 quently but probably in immediate connection with the folding. 



(,'i a i ral Structure. < lohsideration of the unconformities of the Taylor- 

 ville section and of the structure of mount Jura prepares the way for a 

 closer analysis of the structure of the whole region. 



A.8 already stated, the strike of the strata is approximately northwesl 



► The curvature of the faull -ml' is indeed con i ile, bul in this it does nol differ from 



the major faults of the Scottish Highlands. In mount Jura the relation "t the several parts does 

 nol appe thai of m minoi i uilts, but rather 'tin >renl portions of the same narrow 



zone "i displacemenl . 



