140 ANNALS NEW YORK ACADEMY OF SCIENCES 



South of the Columbus Extension, in the Alta Hecla property, several 

 of these north-south vertical faults are to be seen underground. Pros- 

 pecting along them has failed to develop ore except where the northeast- 

 southwest fissures have been crossed. In every case, these ore-bearing 

 fissures are offset, showing them to be older. The amount of shifting has 

 only been worked out in the one case above cited, as far as known, but 

 generally the displacements are not very great, except in the two large 

 faults already described. 



Summary of Conclusions 



physiography 



(a) The central Wasatch is a maturely dissected block mountain, pre- 

 serving in a modified condition the form of its original profile. 



(h) Before the Wasatch fault was formed, the folded Wasatch forma- 

 tions were planed off by erosion, and several plutonic igneous masses 

 were uncovered, notably the Little Cottonwood granite, the Alta grano- 

 diorite and the Clayton Peak quartz diorite stocks. 



(c) Block-faulting in Tertiai^ time gave rise to the Great Basin 

 ranges, and at the same time the Wasatch block was uplifted. When 

 newly formed, it had a steep vv^estern face and a long gentle eastern back 

 slope. 



(d) The original crest line was the upper edge of the great fault es- 

 carpment on the west. This was also the original divide. 



(e) The divide has migrated from its first position near the western 

 margin to its present position near the eastern margin of the block. The 

 present long west-flowing streams of such canyons as Big and Little 

 Cottonwood are chiefly obsequent streams, being consequent near their 

 mouths. 



(/) The crest line has moved in the same direction as the divide, but 

 only a short distance. 



(g) The Provo and Weber Eivers are probably also obsequent streams 

 in their canyons across the Wasatch. Their head-waters are the eastern 

 consequents that have been captured, so far as the drainage of the 

 Wasatch is concerned. 



(/?) The mature dissection of the Wasatch by stream action was ac- 

 complished before the Pleistocene. Upon the stream-cut topography 

 certain features were superposed due to glaciation during the Pleistocene^ 

 Later modifications have been slight. 



