A PECULIAR BELT OF OBLIQUE FAULTING 



ROLLIN T. CHAMBERLIN 



University of Chicago 



The Rocky Mountain system is a belt of varying structure. 

 Northward from northern Montana it is a sharply delineated chain 

 bordered on its eastern margin throughout many degrees of latitude 

 by great overthrust faults. But in central Montana the regular, 

 linear, faulted chain loses much of its distinctiveness and gives way 

 to an irregular group of scattered mountain clusters.^ Farther 

 south in Wyoming and Colorado the Rockies reassemble in a more 

 definite continuous chain, but in these latitudes folding has replaced 

 faulting as the dominant structure. 



For the present paper it is important to note that in central 

 and southern Montana the Rocky Mountain chain, which else- 

 where constitutes the definite backbone of the continent, spreads 

 out into a plexus of short minor ranges and isolated mountain 

 groups. These reach far out into the Great Plains province, where 

 each of the individual groups becomes essentially a unit by itself. 

 Some have resulted from igneous outbursts, and exhibit the results 

 of vertically acting forces fully as much as horizontal thrusting; 

 others have arisen largely from faulting or folding. In consequence 

 of this diversity of origin of the major features, the general region 

 has been subjected to stresses of quite variable sorts. It is to 

 emphasize the peculiar manifestation of some of these that the 

 present paper is ventured. 



From the vicinity of Billings, in the midst of this region of 

 scattered uplifts, E. T. Hancock has recently described a very 

 remarkable belt of faulting, some 56 miles in length and comprising 

 over 90 separate faults, relatively close together and more or 

 less parallel one to another.^ A striking feature of the belt is that 



' Rollin T. Chamberlin, "The Building of the Colorado Rockies," Jour. GeoL, 

 XXVII (1919), pp. 147-48. 



^ E. T. Hancock, "Geology and Oil and Gas Prospects of the Lake Basin Field, 

 Montana," U.S. Geol. Survey, Bull. 691-D (1918), pp. 101-47. 



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