94 ANNALS NEW YORK ACADEMY OF SCIENCES 



(dip N. 60°), the great canyon holds a general course N. 70° E. for 

 nearly eight miles, slowly truncating the edges of the successively higher 

 beds, which as we go east gradually change their strike toward the south. 

 From its mouth for a distance of about six miles, the canyon is walled by 

 brown and yellowish quartzites interspersed with thick beds of black and 

 purplish blue slates. The upper six miles of the canyon show the post- 

 Cambrian formations, the general continuity of the beds being seriously 

 broken only at one point, opposite South Fork of Mill D. The top of the 

 section passes beyond the northeast divide of the canyon into the north- 

 west corner of the Park City district. 



QUARTZITE-SLATE SERIES 



The great quartzite and slate series is succeeded below by gneiss and 

 schist or granite. The igneous nature of the granite contact was not rec- 

 ognized by the Fortieth Parallel geologists, who mapped the granite as 

 Archean and described the contact as one of sedimentary unconformity. 

 The quartzite succession was assigned to the Cambrian, including the 

 lowermost exposures. In describing the rocks referred to the Cambrian 

 in his recapitulation of the Paleozoic, King"^ says : 



"Thus far among the reported occurrences of the rocks of this horizon in the 

 Cordilleras, the locality at the mouth of Big Cottonwood Canyon must remain 

 as the finest example and the stratigraphical type. The lowest member — the 

 Cottonwood slates, a group about 800 feet thick, which here rests upon highly 

 metamorphic Archean schists — lias thus far yielded no organic forms. The 

 rocks are dark blue, dark purple, dark olive green and blackish argillites, all 

 highly silicious and as a group sharply defined from the light-colored quartzite 

 schists which conformably overlie them. This second group, by far the greatest 

 of the whole Cambrian series, is a continuous zone of schists which have a 

 prevailing quartzite character, though varied with considerable amounts of 

 argillaceous matter. From SCKIO to 9000 feet thick, it has a general uniformity 

 of lithologic condition from Iwttom to top. . . . The prevailing colors of 

 this member are gray, greenish gray, drab and pale brown, never dark colors. 

 Conformably overlying it are 2.500 to 3000 feet of cream and salmon color and 

 white quartzites and quartzofelsites. Occasional sheets of conglomerate are 

 seen in the quartzites not far below the suuunit of the Cambrian." 



A few years later, in the course of his studies of the Cambrian sections 

 of the Cordilleras, Dr. C. D. Walcott^ visited Big Cottonwood Canyon, 

 examining the quartzite series in more detail and re-measuring the sec- 



■^ C. King : U. S. Geol. Expl. 40th Par., Vol. I, pp. 220-2.30. 1878. 



8C. D. Wal^ott: "Second Contribution to the Studies on the Cambrian Faunas of 

 North America." Bull. U. S. Geol. Surv. No. 30, pp. 38-39. 1886. 



