30 THE ROYAL SOCIETY OF CANADA 



Other sandstones at the base of the formation may owe their 

 marine deposition to this same reassorting action of the incoming sea 

 on the loose material covering the consolidated rocks. Few exposures 

 of these lower beds occur ; but the evident marine character of some 

 of the upper members of the Tar sands on the Athabaska may have 

 been due to this action. 



The close of the Colorado stage was marked by a change in the 

 fauna and it has been suggested that there was also an erosion interval. 

 This seems not to have been definitely proven ; but erosion by currents 

 may account for variable thicknesses in the thin sands at the outer 

 edge of the covering shore deposits. The extinction of several species 

 of marine life may also be taken as a proof of the almost complete 

 retreat of the sea; or the change of fauna may have some connexion 

 with the fact that the Colorado sea communicated with Arctic and 

 subtropical waters, while during the succeeding Montana submergence 

 it is doubtful if any northern waters were admitted. 



THE MONTANA GROUP. 



The deposits of the marine period which succeeded the Colorado 

 stage have been classified in ascending order as the Pierre shale and 

 the Fox Hills sandstone. The succeeding brackish water member, 

 the Lance, owing to the inclusion in it of marine beds, is held to be of 

 Cretaceous age. It forms in northern Dakota the latest deposits 

 in the near vicinity of salt water and resembles the shore deposits of 

 Alberta. As it contains a vertebrate fauna of more modern type 

 than those of the latest brackish water beds of Alberta, the Edmonton, 

 its position above the Montana beds, the Fox Hills sandstone, would 

 intimate that in the absence of the Fox Hills in Alberta the top of 

 the Montana should include at least the Edmonton. 



But as there are beds beneath this latter formation which carry 

 a Fox Hills fauna and have been correlated with it the question has 

 arisen as to the possibility of the Edmonton beds being Laramie, as 

 originally described in the reports for 1882-86. The name Laramie 

 was then used in a broad sense to denote beds that formed a transition 

 series between the Cretaceous and Tertiary. Latterly the name has 

 been restricted to a single area and a set of beds whose position re- 

 lative to the top of the Cretaceous is not firmly established. The 

 definition Laramie for any deposits in Canada is, therefore, of little 

 value and the only attempt at a correlation of the Edmonton with 

 other beds will be to show its relation to the highest beds of the 

 Cretaceous in the eastern areas such as Saskatchewan and Dakota. 



