NO. lO DISCOVERIES OF CAMBRIAN BEDS RESSKR 9 



syncline, which follows the trend of the northern Rockies south from 

 their northern extremity to Montana, where it swings westward 

 around the Southern Rcjcky Mountain region and thence continues 

 southwestward through the Great Basin, to enter the Pacific in southern 

 California. Or possihly one might consider this as two geosynclines 

 joined hy a crossover in Montana ; hut the faunas in hoth are the same. 



By Middle Camhrian time floods apparently penetrated the entire 

 length of this long negative area. It is not to he understood that all 

 Middle Cambrian formations are thought to have covered the entire 

 width and length of the geosyncline, for they were evidently deposited 

 in relatively narrow, often parallel, and always very shallow troughs, 

 and dififerential movements within the larger depressed area must have 

 operated everywhere and during all time so that every formation \\as 

 a discontinuous sheet. (See Walcott, 1927.) 



With the beginning of Upper Cambrian time, subsidence a])pears 

 to have alTected the whole continent to such an extent that marine 

 A\-aters were enabled not only to tlood portions of this long geosyn- 

 cline, but also to extend themselves out across the smoothed surfaces 

 of interior portions of North America. Thus in the Southern Rocky 

 Mountains Cambrian seas were able to enter the basins between certain 

 positive elements which were then islands and are now the cores of 

 existing ranges. It seems that possibly all of the Cordilleran geo- 

 syncline was drained at the close of Middle Cambrian, because the 

 basal Upper Cambrian beds usually contain salt crystals, ripple marks, 

 and other shallow-water features. On the other hand, relatively soon 

 after the seas reached their maximum extent in lower Upper Cambrian, 

 emergence began west of the Mississippi Valley, so that the younger 

 members of the Cambrian are less and less widely distributed. With 

 no change in dip, the Mons, Garden City, Manitou, or equivalent 

 formations again spread widely both within and without the geosyn- 

 cline, overlapping the Cambrian beds of various ages but apparently 

 never reaching beyond them to rest directly on the Cryptozoic. In 

 other words, diastrophic movements creating early Paleozoic basins 

 or geosynclines were fully determined by early Upper Cambrian. 



REFERENCES 

 Branson, C. G. 



1931. New paleontologic evidence on the age of the metamorphic series of 

 northeastern Washington. Science, n.s., vol. 74, p. 70. 

 Daly, R. A. 



1912. Geology of the North American Cordillera at the Forty-ninth Paral- 

 lel. Geol. Surv. Canada Mem. 38. 



