366 . DESCRIPTIVE GEOLOGY. 



the strike of these beds, while that cailoii itself, above the bend, has been 

 carved ont of the Weber Quartzite. No good section of this formation is, 

 however, obtained here ; various beds of white quartzite, and some of an 

 iron-stained quartzitic sandstone, are exposed at various points on either 

 side, but the canon is encumbered with debris and moraine material. Near 

 the bend, the latter forms a high ridge on its western side, through which 

 the present course of the stream has been cut. On the ridges just north of 

 this bend, in the continuation of the course of the old glacier- canon, heavy 

 bodies of white quartzite are exposed ; but, as at this point the formation 

 makes a sharp bend to the westward, and the beds are consequently twisted 

 and faulted, no opportunity for estimating the thickness is given. An anal- 

 ysis of the pure white quartzite from this canon gives nearly 9') per cent, 

 of silica, the other constituents being lime, alumina, and a trace of oxide 

 of iron. 



Cambrian Formation. — In the section exposed along Big Cottonwood 

 Canon is afforded the best opportunity for seeing the rocks of the Cam- 

 brian formation, but even there it is difficult on the ground to form a satis- 

 factory estimate of its thickness, as the canon is cut so obliquely to the 

 strike, and in part runs with it, while bending in every direction. In gen- 

 eral, it may be described as a body of quartzites more or less argillaceous, 

 having some fine-grained mica-schists in its upper portion, and, near the base 

 of the part exposed, a bed of some 800 feet of dark-blue, almost black, finely- 

 laminated argillites. Its thickness, as estimated from the distances between 

 outcrops and the average dip, cannot be less than 12,000 feet. 



In descending the canon from the bend, a thickness of from 2,000 to 

 3,000 feet of white quartzite is crossed, containing some beds of limestone, 

 then a series of white crystalline limestones, with some bluer strata, still 

 crystalline, in the upper part of which are the dike and granite body, 

 already described. Limestone exposures are found down as far as the 

 mouth of a little canon coming in from the north, where is the lowest body 

 of limestone found. The Ogden Quartzite is not distinctly recognized in the 

 canon, being obscured by surface accumulations. This limestone, however, 

 resembles the Silurian of Little Cottonwood in containing needle-like 

 crystals of tremolite, which are visible to the naked eye. On the ridge to 



