13-t 



ANNALS NEW YORK ACADEMY OF SCIENCES 



eral Flat. The lowest overthmst member is quartzite, plainly seen as 

 the capping of Bald Mountain directly south of Alta (see geologic map, 

 Plate VI). All along Peruvian Gulch and in American Fork, this 

 seems to lie conformably upon the limestone. Both the limestone and 

 the quartzite being very resistant, the contact is often sharp with very 

 little crumpling or brecciation. The truncation of the beds, however, 

 shows beyond any doubt the secondary nature of the structure. More- 



Argenta 

 N w 



Alta 



S E 



FIG. 5. SECTION BETWEEN ARGENTA, IN BIG COTTONWOOD CANYON, AND ALTA, IN LITTLE 



COTTONWOOD 



Relation of the overthrust Paleozoic and Proterozoic strata to beds of the same ages 



below 



1 = Algonkian quartzite. 2 = Algonkian "conglomerate." 3 =: Cambrian quartzite 

 4 = Cambrian shale. 5 ^ Ordovician and Devonian limestones. TT'=: Thrust surface 



over, in many places crumpling and brecciation have occurred — as should 

 be expected. In all such cases, the limestones have been the least af- 

 fected, but the overthrust quartzites and shales have suffered strong 

 deformation. The best example of this condition is seen on the slopes 

 northwest of Alta. The black Cambrian shale has here been drawn out 

 into a long tongue in the midst of the quartzite, showing every inclination 

 from strongly overturned folds near the Columbus mine to a vertical posi- 

 tion farther up the hill. The quartzite is folded and smashed in such a 

 way as to" be chaotic, individual blocks being traceable for short distances 

 only. 



