OVERTHKUSTS NEAR OGDEN 



537 



a thick slab of the Cambrian quartzite lies above the thrust-plane, and 

 the Middle Cambrian limestones are beneath it. That the thrust-plane 

 is not confined to a particular horizon is shown by two facts: (a) The 

 underlying limestone is but 200 to 300 feet thick at one point on the 

 front of the range, but is nearly 3,500 feet thick along the bottom of the 

 canyon, and (h) the overlying quartzite is but a few hundred feet thick 

 east of North Ogden, but is complete, and even carries a wedge of 

 Archean gneiss beneath it in Ogden Peak.^^ The weak, shaly Middle 

 Cambrian limestones just below the overthrust are intensely folded, the 

 folds being mashed flat parallel to the general bedding. Thinning on 

 the limbs and thickening on the crests of the folds are conspicuous. Only 

 suggestions of such structures can be seen in the limited exposures along 



a minor 

 overthrust 



V/il/ard 



overthrust 



Algonkian 



'en overthrust 



slafe 





Figure 7. — Diagram to the Geology and Structure loithin the Scope of Figure 2, Plate 39 



the bottom of the canyon, but they are in plain view from the south rim 

 of the valley. From Ogden Canyon this overthrust runs south along the 

 front of the range, bringing Archean gneiss out upon the Cambrian lime- 

 stone. It sinks again into the Salt Lake plain before reaching Weber 

 River. 



It may be said in passing that there is a smaller, but nevertheless im- 

 portant, overthrust near the top of the quartzite formerly called the 

 "Ogden." A sliver of the quartzite with the overlying shale and lime- 

 stone has overridden the Middle Cambrian shale with a little of the lime- 

 stone, thus making a second repetition of those beds. It does not reach 



^ To the people of this region Ogden Peak is linown as "Observatory Mountain." 



