PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 175 
(St. Regis formation, 1,000 feet—Shales and quartzites of pre- 
vailingly green and purple tints with shallow water markings 
Revelt quartzite, 1,200 feet—Thick bedded, in part sericitic, 
but mostly clean quartzite 
Burke formation, 2,000 feet—Fine-grained, light-colored, thin- 
bedded siliceous quartzites and shales . 
Ravalli group 
Crawford and Worcestet™ report that the pre-Cambrian rocks 
of the Gold Brick district of Gunnison County, Colorado, include 
mica, cordierite-mica, garnet, amphibole, quartz, granitic, and 
hornblendic schists of which some are probably altered sediments. 
Quartzites and pyroxenic quartzites, quartzite conglomerate, 
andalusite quartz rocks, and epidote rocks also occur. Certain 
granite and diorite intrusion are probably pre-Cambrian. 
Exposures of quartzite and schist or shale? belonging to the 
Algonkian Uncompahgre formation are found in the Piedra Canyon 
of the San Juan region. 
Darton} states that granite is the pre-Cambrian rock of Luna 
County, New Mexico. 
Darton‘ reports that the pre-Cambrian rocks of the Deming 
quadrangle of southern New Mexico consist of granite with subor- 
dinate gneissic granite and diorite. 
Duncan® describes the pre-Cambrian rocks of Harney Peak, 
South Dakota, as consisting of mica, hornblende, garnet schists 
intruded by granite and associated with greisen, pegmatite, and 
quartz veins. 
The Philipsburg quadrangle® lies in the central western part of 
Montana. The Belt series is unconformably overlain by the 
tR. D. Crawford and P. G. Worcester, ‘‘Geology and Ore Deposits of the Gold 
Brick District, Colorado,” Colorado Geol. Surv. Bull. 10 (1916), 116 pp., 9 pls., 4 figs. 
2 Whitman Cross and E. S. Larsen, ‘‘Contributions to the Stratigraphy of South- 
western Colorado,” U.S. Geol. Surv. Prof. Paper 90 (1914), pp. 39-50, 1 pl., 2 figs. 
3N. H. Darton, ‘Geology and Underground Water of Luna County, New 
Mexico,” U.S. Geol. Surv. Bull. 618 (1916), 188 pp., 13 pls., 15 figs. 
4N. H. Darton, ‘Description of the Deming Quadrangle, New Mexico,” U.S. 
Geol. Surv. Geol. Atlas, Folio No. 207 (1917), 15 pp., 5 pls. (maps and illus.), 11 figs. 
5 Gordon A. Duncan, ‘‘Contribution to the Study of the Pre-Cambrian Rocks 
of the Harney Peak District of South Dakota,” Trans. Am. Inst. Min. Eng., Vol. 
XLIII (10913), pp. 207-18, 3 figs. 
_ ©W. E. Emmons and F. C. Calkins, ‘‘Geology and Ore Deposits of the Philips- 
burg Quadrangle, Montana,” U.S. Geol. Sur., Prof. Paper 78 (1913), 271 pp., 17 pls. 
