lOi ANNALS NEW YORK ACADEMY OF SCIENCES 



black conglomerate already referred to as occurring at the head of South 

 Fork. The conglomerate is nowhere of ver}^ great thickness, being usually 

 less than 10 feet. Within the lower 200 feet of the succeeding quartzite 

 are several sheets of fine conglomerate, the pebbles being quartz and 

 quartzite. The remaining 500 feet are of coarse white quartzite which 

 weathers to a light yellow or cream color. Ft is well bedded into layers 

 varying from a few inches to several feet in thickness. Toward the top, 

 the beds become uniformly thinner and gradually pass into shale, the 

 latter being intercalated between the thin sheets of quartzite. Hanging 

 from the under side of several quartzite layers in this transition zone are 

 curious Arthrophycus-like structures. The sandy shale layers show well- 

 preserved ripple marks of the parallel types, proving the shallow water 

 origin of these sediments and their transitional character. 



A similar quartzite formation is of wide occurrence in the Wasatch 

 Range to the north and south and in the Basin ranges to the west. It is 

 everywhere very similar in its appearance and physical characteristics and 

 is followed by a dark shale of Lower or Middle Cambrian age. From its 

 occurrence near Brigham City, Utah, Walcott has called it the Brigham 

 quartzite, and though it is better shown at Willard and several other 

 places along the range, we may retain the original name to avoid repeti- 

 tion. In Big Cottonwood Canyon, it is well exposed just below the old 

 Maxfield mine and may be seen on both walls of the canyon. Southward, 

 it becomes the east wall of Mineral Fork, underlying the limestone and 

 shale which form the capping of Kesslei*^s Peak. Dipping to the north- 

 east, it cuts across the head of South Fork and crosses the divide into 

 Little Cottonwood Canyon just north of Alta. 



Overlying the Brigham quartzite, just at the Maxfield mine, is a dark 

 micaceous, sandy shale, which, from its prominence just at the little town 

 of Alta, we may call the Alta shale. It rests conformably on the Brigham 

 quartzite with which it is in bold contrast on account of its black color. 

 It is somewhat variable in thickness, ranging from 150 to 200 feet. From 

 a sandy character near the base, it passes slowly into a thinly bedded, fine- 

 grained shale in the middle and upper part, representing a continuous 

 depositional unit. From two horizons within the Alta shale, 100 feet 

 apart, Walcott^* reports the following Middle and Lower Cambrian fauna 

 from Big Cottonwood Canyon : 



i< C. D. Walcott : U. S. Geol. Surv. Bull. No. 81, p. 319. 1891. 



