AQUI MOUNTAINS. 459 



western dip, while in the narrow gorges a few miles from the mouth, the dip 

 varies from perpendicular to 60° to 70° eastward. It may be supposed that 

 the anticlinal axis here lies somewhat to the east of the main ridge, and that 

 the break has followed a line a little to the west of it. Whether this suppo- 

 sition be correct or not, it is evident that in this portion of the range the forces 

 of contraction and dislocation have acted most powerfully. It- is worthy 

 of remark that the line of the southern general section on the map crosses the 

 Wahsatch, Oquirrh, and Aqui Mountains approximately at the points of the 

 most violent disturbances in the sedimentary beds, and where the develop- 

 ment, both of the older granites and porphyries and of the younger volcanic 

 rocks, has been most considerable; it also indicates, in the two former, the 

 region of the greatest concentration of argentiferous minerals; in the latter, 

 these have not yet been developed. 



On the western foot-hills of the range, the quartzites can be traced as 

 far north as Hooper's ranch, where they form an outlying hill, the northern 

 point of which is formed of steeply-dipping limestone beds, having a strike 

 somewhat to the east of north. The limestone beds further north, on the 

 west of Grantville Peak, were observed resting on the westerly-dipping 

 quartzites, but their southern limit was not definitely determined. 



Grantville Peak forms the crest of a sharp anticlinal fold, whose western 

 member dips about 45° west, while the eastern beds are upturned at mucli 

 steeper angles, assuming at the extreme foot-hills a perpendicular position 

 like those on the east of Bonneville Peak. The lowest beds exposed here 

 ate the same quartzites that were found at that peak, and likewise form the 

 highest portion of the ridge. The purple quartzite with flattened pebbles 

 is particularly noticeable, forming the surface of the saddle north of Grant- 

 ville Peak, and of the eastern slopes, where the force of the strong west 

 winds, blowing from the desert, has laid bare and polished its surface, and 

 worn away the matrix of the rock, leaving the harder pebbles standing out 

 in rounded knobs. The whole series from the Cambrian to the Lower Coal- 

 Measure limestone have been indicated here, as there was no evidence of 

 any faulting. To the north, the beds sink, and the angle of dip becomes 

 less steep ; to the northeast of Grantville Peak, the outlying foot-hills show 

 limestone beds dipping from- 25° to 45° to the east and north, while the 



