THE BANNOCK OVERTHRUST TO] 
The additional possibility should not be overlooked that the 
known thrusts of probably identical age lying to the east and to 
the west may in reality bound portions of the same overthrust 
mass which have been isolated by erosion. 
North of the region of the Bannock thrust and in what appears 
to be the same zone of crustal readjustment, faults of great magni- 
tude are known to exist. One in Montana, on the east side of the 
Bitterroot Mountains, has been described by Lindgren (1s), 
another in the vicinity of Philipsburg, Montana, by Calkins (7), 
and the Lewis thrust in northern Montana and southern British 
Columbia which has been described by McConnell (16), Willis 
(27), and more recently studied by Campbell. 
The last two are clearly thrusts the planes of which have been 
deformed, and all three may eventually prove features of the same 
tectonic event as the Bannock and the parallel faults toward the 
south, although it appears that if Willis’ age determination of the 
Lewis thrust is correct, the Bannock overthrust occurred at an 
earlier geologic date. 
It is apparent, however, that a close approximation of the 
actual and relative ages of the several faults awaits more extended 
geologic studies in the Rocky Mountain region. 
BIBLIOGRAPHY 
1. Blackwelder, Eliot. ‘‘New Light on the Geology of the Wasatch Moun- 
tains, Utah,” Bull. Geol. Soc. America, XXI (1910), 517-42; (@) Pp. 523; 
(0) p. 527; (c) p. 526; (d) p. 532; (€) p. 520; (f) p. 528. 
2 “Phosphate Deposits East of Ogden, Utah,” Bull. U.S. Geol. 
Survey No. 430 (1910), pp. 536-51. 
ae “Reconnaissance of Phosphate Deposits in Western Wyoming,” 
Bull. U.S. Geol. Survey No. 470 (1911), pp. 452-81; (a) p. 450. 
4. Boutwell, J. M. “Stratigraphy and Structure of the Park City Mining 
District, Utah,” Jour. Geology, XV (1907), 434-58; (a) p. 444. 
“Geology and Ore Deposits of the Park City District, Utah,” 
Prof. Paper U.S. Geol. Survey (in preparation). 
6. Breger, C. L. “The Salt Resources of the Idaho-Wyoming Border, with 
Notes on the Geology,” Bull. U.S. Geol. Survey No. 430 (1910), pp. 555-60; 
(a) p. 562. 
