4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



these ranges were apparently deposited in a geosyncline, and the 

 contained faunas indicate their deposition in the seas covering the 

 Great Basin. In other words this situation would naturally be expected 

 if these ranges are the eastern margin of the Great Basin geosyncline. 



The manner in which Cambrian distribution is related to the struc- 

 tural provinces is well shown in the Beartooth region. On the south 

 and east sides of this dome Upper Cambrian strata of the Deadwood 

 series rest directly on the peneplaned Cryptozoic, but on its north- 

 western flanks the older Middle Cambrian holds this relationship. 

 This situation extends the Middle Cambrian shore line, described by 

 Peale for the southern margin of the Gallatin Valley, a considerable 

 distance toward the east. 



Northern Rocky Mountains. — From the Beartooth Mountains in 

 southern Montana, immediately northeast of the Yellowstone National 

 Park, northward to the Yukon River in northern Canada, all ranges 

 of the eastern Cordilleran element may be grouped as the Northern 

 Rocky Mountains. Again, from the standpoint of Cambrian or early 

 Paleozoic history, this usage departs from that of some physiographers, 

 conforming more closely to that of Daly, who regards the Rockies as 

 confined, in an east-west direction, to the mountains between the 

 Great Plains on the east and the Rocky Mountain Trench on the west. 



In contrast to conditions characterizing the Southern Rockies, the 

 northern subdivision consists essentially of great thicknesses of folded 

 and faulted sediments, evidently deposited in geosynclines. These 

 geosynclines were, of course, the result of prevailingly negative move- 

 ments, which allowed the accumulation of thicker, more continuous 

 sedimentary series than were possible in basins of the Southern 

 Rockies. 



In the southern portion of the Northern Rockies, as stated above, 

 the Gallatin, Madison, Jefferson, and McCartney Ranges exhibit 

 Cryptozoic cores, on whose peneplaned surface Middle or Upper 

 Cambrian strata rest without intervening Beltian beds, in which re- 

 spect they assume characteristics of the Southern Rockies. However, 

 only a few miles north of the mentioned ranges Beltian strata lie 

 beneath the Cambrian, and continuing northward the Beltian at once 

 thickens rapidly, covering most of northwestern Montana and ex- 

 tending into Canada beyond the Watertown Lakes Park. It has been 

 estmiated that these Beltian strata total fully 60,000 feet. For a long 

 time it was thought that this enormous thickness of sedimentary 

 deposits constituted the complete sedimentary record of the geosyn- 



