PHYSICAL AND FAUNAL EVOLUTION S3 



and regular one, but also necessitates the further assumption of an 

 enormous erosion during the succeeding transgressive movements, 

 which not only removed the greater part of several thousand feet 

 of strata over the northern United States area, but also the whole of 

 the extensive Canadian deposits of Beekmantown which must have 

 reached far toward the Arctic regions, if the entire Beekmantown was 

 deposited as a transgressional series. Aside from the fact that erosion 

 would scarcely be very active during a positive diastrophic movement 

 or transgression of the sea, it can hardly be assumed that such exten- 

 sive erosion preceded the deposition of the St. Peter sandstone and 

 the Chazy formation. Moreover, the intimate relation between the 

 Lower St. Peter and the underlying Lower Beekmantown demands 

 a close succession in deposition, the lower sand beds being probably 

 deposited by the shoaling sea itself. If that is indeed the case, no 

 higher dolomites of Beekmantown age than are now found ever 

 existed in the Minnesota area. 



West of the Rocky Mountains, the basal Uinta quartzite is chiefly if 

 not wholly a continental deposit of pre-marine Cambric time, 12,000 

 feet or more in thickness. Upon this enormous basement series the 

 eastward-transgressing Cambric sea laid down its progressively over- 

 lapping strata, the upper beds of the series being reworked during the 

 progress. The transgressing sea apparently did not reach the region 

 of the eastern Uintas, where the basal ciuartzhe is succeeded by the 

 Ivodore shales. From these shales Powell reported Carboniferous 

 (Mississippic ?) fossils,' and he gives evidence of the existence of a 

 disconform.ity between these shales and the basal sandstone. Weeks^ 

 identifies the Lodore with the Iron Creek shales of Berkey, which lie 

 between the Uinta and the so-called Ogden^ cjuartzites, and which 

 Berkey correctly correlates with the Cambro-Ordovicic Ute limestone 

 of the Wasatch. Weeks fails to recognize that, as Berkey has shown, 

 the "Ogden" quartzite has united with the Uinta in the eastern section, 

 the intervening shales having wedged out. The Lodore of the eastern 

 LTintas thus lies above the "Ogden" horizon, and corresponds to a part 

 of the overlapping Mississippic series (see Fig. 6). 



The Lower Ordovicic retreat is shown in the western section by the 



I Geol. of the Uinta Mountains. ^ Bull. Geol. Sac. Amer., Vol. XVIII, pp. 435. 436- 



sBlackwelder has recently shown that the "Ogden" of the Uintas is not the true 

 Ogden. 



