174 EDWARD STEIDTMANN 
metamorphosed sediments consisting of quartzites, slates, dolo- 
mites, lava flows, pyroclastics, and tillites. Detailed studies have 
been made. 
Butler and Loughlin' report that the pre-Cambrian rocks of 
the Cottonwood—American Fork mining region of Utah, south- 
west of Park City, consists mainly of shallow-water deposits of 
quartzites, schists, and slates about 11,000 feet thick. They dip 
steeply to the north. At the top of the section is a conglomeratic 
layer resembling tillite. 
The St. Joe-Clearwater’? region of Idaho, comprising about 
250 square miles, lies about 30 miles to the southeast of the Coeur 
d’Alene lead-mining district. The Algonkian sediments exposed 
in this area include mica schists and quartzites which are correlated 
with those of the Coeur d’Alene district. The base on which they 
rest is not exposed. The formation of this area which is correlated 
with the St. Regis of the Coeur d’Alene lacks the purple color 
assumed to be characteristic in the type locality. The most 
difficult correlation was that of the beds believed to correspond to 
the Newland formation, since they are many times thicker than 
in the Coeur d’Alene district. 
The region around Mullan, Idaho, and Saltese, Montana,3 over- 
laps the southeast part of the Coeur d’Alene quadrangle. The 
pre-Cambrian rocks exposed belong to the Algonkian belt series 
and include the following formations: 
Striped Peak formation—Chiefly greenish gray and some purple beds of shale 
and sandstone with shallow water markings 
(Blue shale of variable thickness—s,o00 feet 
| to insignificant. Blue- and white-banded 
Newland (Wallace) J argillite with some greenish beds, with 
formation . . . ned aces some limestone beds. Chiefly green colored 
| calcareous rocks with argillaceous beds 
1B. S. Butler and G. F. Loughlin, “‘A Reconnaissance of the Cottonwood— 
American Fork Mining Region, Utah,” U.S. Geol. Surv. Bull. 620 (1915), 
pp. 165-226, x pl. 
2 F.C. Calkins and E. L. Jones, Jr., ‘‘Geology of the St. Joe—Clearwater Region, 
Idaho,” U.S. Geol. Surv. Bull. 530 (1913), pp. 75-86, 1 pl. 
3 F. C. Calkins and E. L. Jones, Jr., ‘Economic Geology of the Region around 
Mullan, Idaho, and Saltese, Montana,” U.S. Geol. Surv. Bull. 540 (1912), pp. 167-211, 
1 pl. (map). 
