[dowling] cretaceous SEA IN ALBERTA 29 



of the Colorado group and sometimes well down in what would seem 

 to be the Benton. This is well shown in the cores obtained from the 

 Moosejaw well. In Alberta there can be no division of the Colorado 

 on lithological grounds. 



In a discussion of the formation near the typical locality of the 

 Benton formation, T. W. Stanton says/ "In the neighborhood of Fort 

 Benton and in all the region now under investigation there is no 

 limestone corresponding to the Niobrara, and there is no evidence 

 of an erosion interval or unconformity; it is probably represented 

 by shales or sandstones. The Palseontologic indications are that 

 in this region the Niobrara is represented by dark shales not separable 

 stratigraphically from the Benton. If this is true the Benton shales 

 of the upper Missouri represent more than the formation known 

 by the same name in Nebraska, in Colorado east of the Front Range, 

 and at other places, and really include the whole of the Colorado 

 group so that it is more appropriate to call them Colorado shales, as 

 Weed has done in the Fort Benton folio." 



In the Alberta exposures the only evidence of a possible sub- 

 division other than by a critical study of the fauna is the occurrence 

 of thin sandy layers about the middle of the formation, which near 

 the mountains in many places develop into quite thick members 

 (Plate II). In the Blairmore section the sandstone bed is used as a 

 horizon marker and is overlain by sandy shales 150 feet thick. It 

 is here below the middle of the formation, the upper part of which 

 is thickened locally. Farther north, sandstones in the Benton are 

 found on the Athabaska at the Grand rapids and a similar series on 

 Peace river. The Peace River sandstones are observed to thin out 

 materially toward the east and finally die out. These sands may 

 not denote a divisional line between the beds which are elsewhere 

 called Benton and Niobrara; but they seem rather to denote a period 

 in this great sea when the western margin was shifted to the east for 

 a short period, or a slight shallowing of the sea accompanied by re- 

 newed denudation of the land area to the west. This is the only 

 indication, in the deposits, of a possible western limit to the first 

 advance of the Cretaceous sea. The mid-Colorado sands of the Peace 

 and Athabaska rivers are curiously suggestive of an elevation of the 

 land area within or near which the highest peaks of the Rocky moun- 

 tains are located, and suggest not so much the early building of these 

 masses as an early lifting and formation of a land area previously 

 covered by the unconsolidated continental deposits of the early 

 Cretaceous and the rapid denudation and re-assortment of this loose 



material on the sea floor. 



1 Geology of Judith River beds. Bull. U. S. G. S. No. 257. 



