PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 177 
The Belt series,? according to Walcott, unconformably underlies 
the Middle Cambrian Flathead quartzite. In ascending order 
the members exposed are the Spokane shale, Empire shale, Helena 
limestone, and Marsh shale. The total thickness is 3,300 feet at 
Helena, of which the Helena limestone comprises 2,400 feet. 
Knopf and Kirk? report that pre-Cambrian rocks underlie with 
marked erosional unconformity the Lower Cambrian of the Inyo 
range of southern California. The pre-Cambrian system from the 
top downward consists of the following: 
Deep Spring formation—Local sandstone and dolomite beds, 1,600 feet 
Reed dolomite—2,000 feet 
? Sandstones and thin-bedded, impure dolomites, 2,000 feet (?) 
Both Archean and Algonkian3 are exposed in the Shinumo 
quadrangle. They are separated by a well-marked unconformity 
characterized by angular discordance of structures, difference in 
metamorphism, and intrusives. 
The Archean is composed of the Vishnu schists including quartz, 
mica, and hornblende schists. They are cut by Archean quartz 
diorite and granite pegmatite intrusives. 
The Algonkian section is as follows: 
Unconformity 
Dox sandstone—Cross-bedded, ripple-marked in part, mud-cracked argilla- 
ceous layers. 2,297 feet plus unknown thickness removed 
by pre-Cambrian erosion 
Shinumo quartzite—Hard, compact, cross-bedded sandstone and quartzite, 
usually of fine and even grain. 1.564 feet 
Hakatai shale—Argillaceous red shale grading upward into arenaceous red 
shale and sandstone. Nearly all beds contain sun cracks 
and ripple marks. Metamorphosed by a thick diabase 
sill. 580 feet 
t Adolph Knopf, ‘‘Ore Deposits of the Helena Mining District, Montana,” U.S. 
Geol. Sur. Bull. 527 (1913), 143 pp., 7 pls., 4 figs. 
2A. Knopf, ‘“‘A Geologic Reconnaissance of the Inyo Range and the Eastern 
Slope of the Southern Sierra Nevada, California,”’ with a section on the stratigraphy 
of the Inyo range, by Edwin Kirk, U.S. Geol. Surv. Prof. Paper 110 (1918), 130 pp., 
32 pls., 8 figs. 
3 L. F. Noble, “The Shinumo Quadrangle, Grand Canyon District, Arizona,” 
U.S. Geol. Surv. Bull. 549 (1914), 100 pp., 18 pls. (incl. map in pocket), 1 fig. 
