CAMBRIAN FORMATION. 367 



the north of the head of this canon is found the main body of the Wahsatch 

 limestone, with the following characteristic Coal-Measure fossils : 



Chonetes granuUfera. 



Froductus Nehrascensis. 



Productus pertenuis? 



Productus symmetricus f 

 It is, in general, much less crystalline than in the main canon, and 

 already strikes nearly west, with a dip to the northward. 



In the main canon, immediately below the Ute limestone, is a thickness 

 of some 200 feet of schistose rock, quite micaceous near the bottom, then 2,000 

 to 3,000 feet of various quartzites, crossing the canon at an oblique angle ; 

 that found in the Three Lake Canon, Avhich has been so largely polished 

 and striated, contains only 60 per cent, of silica, the other constituents 

 being mostly alumina, with a little lime and iron ; then, to the mouth of the 

 caiion, argillites and quartzites, with every intermediate gradation, among 

 which was observed, near the summit of Twin Peak, a bed of micaceous 

 quartzite or mica-schist, in which the mica occurs rather sparsely in very 

 fine specks, but sufficient to impart in places a schistose structure to the 

 rock. The peak next east of Twin Peak is formed of dark-blue argillaceous 

 slate, in which there is some development of bronze-colored mica in small 

 crystals, not sufficient, however, to affect the character of the rock. In 

 Plate XVI, a view taken about opposite Twin Peak in a bend of the main 

 canon, where its course has been deflected to the south by a body of harder 

 slates, the characteristic forms of these rocks are well illustrated. The mass 

 of Twin Peak is hidden by the spur in the left foreground, but the side- 

 canon behind these spurs leads up to its northern base. It is, however, 

 almost inaccessible from this side, and more easily ascended from the east. 

 Near the mouth of Big Cottonwood, a body of dark-blue or black argil- 

 lites crosses the canon, and abuts up against the little granite body, in the 

 side-canon on the south. In the ridge which separates this canon from that of 

 Mill Creek, all these strata bend from a northwest to an east and west strike, 

 with many folds and changes of dip, and are seen in section along the foot- 

 hills of the range standing at a very steep angle, over 50° to the north. 

 The section of the Cambrian body as thus exposed, extending north from 

 the mouth of Big Cottonwood a distance of about 4 miles across the strike, 



