34 THE ROYAL SOCIETY OF CANADA 



Upper Pierre shore and marine deposits, i.e. Edmonton and 



Bearpaw. 

 Lower Pierre shore and marine deposits, i.e. Belly River. 



Later investigation may correlate these with the Odanah and 

 Millwood shales of Manitoba. 



LOWER PIERRE. 



The first advance of the Pierre sea although reaching probably 

 farther north than in the second return did not in southern Alberta 

 and northern Montana advance as far west. In the foothills there are 

 areas giving sections of the shore deposits of that time in which but 

 traces of the marine beds of the early invasion are to be found. This 

 section, including all the lower Pierre shore deposits, is undoubtedly 

 the group described by Dawson as the Belly River series. In the east- 

 ern exposures of the formation near Milk river the lower Pierre marine 

 shales cut into the Belly River series and only about half of the section 

 is exposed. The exposures of the Belly River rocks occurring on the 

 South Saskatchewan in the vicinity of the mouth of the Bow river, 

 contain marine types of fossils in a dark clay shale that seems to be a 

 portion of the Lower Pierre deposit. As this is included in the Belly 

 River formation it seems that both shore-formed beds and those of 

 marine deposition, within certain limits, are to be considered as be- 

 longing to the Belly River formation. 



Lower Pierre (Belly River) Lower Shore Deposits.' 



The first advance of the Pierre sea over the surface covered 

 by the Colorado deposits may have in some places been slow enough 

 for the denudation of some of the surface, since denudation of the upper 

 beds of the Niobrara is recorded by Meek and Hayden.^ 



There is no mention of this erosion having been found in the 

 western exposures and there seems to be no evidence of the time 

 interval except perhaps the change in fauna. The advance seems to 

 have been checked before it reached its farthest bounds or occurred 

 at a time when much coarse-grained material was being carried to 

 the western margin from the land area. These shore deposits where 

 they are best developed have all the characters which point to their 

 being deposited in a slowly receding sea and again quickly covered 

 (see Plate IV). 



1 See p. 65, Bull. U. S. G. S. No. 257. 



