85 



In the west the marginal beds below the marine Cretaceous 

 sediments are as a rule fresh water deposits. The coarse 

 conglomerates and sandstones, there found belonging 

 to this period of extension of the Cretaceous sea, indicate 

 some corresponding uplift in the land area to the west 

 which increased the gradient of the slopes. The coarse- 

 ness and thickness of the material contained in these 

 beds (maximum 6000 feet, 1824 m. in Crowsnest area, 

 reduced rapidly to the east to less than 900 feet (274 m), 

 suggest a nearer approach to the zone in which mountain 

 building was active, probably in the southern part of the 

 present western Rocky mountains. 



Throughout the later stages of the Cretaceous, the 

 eastern part of the basin shows little change in the 

 deposits which were mainly marine clays. The western 

 part, as exposed in the deposits of the faulted zone, shows 

 repeated subsidences and elevations up to sea level. Active 

 denudation of the western land areas is shown in conglomer- 

 ates at the top of Benton shales exposed on Bow river and 

 northward on the Brazeau and Athabaska rivers. Con- 

 glomerates also occur in the Belly River series at Crows- 

 nest mountain and in the north in the Brazeau fields. 

 This material was probably eroded from the hills appear- 

 ing to the west, the prototypes of the western portion 

 of the Rocky mountains. 



The periods of elevation along the western margin 

 of the interior region with the consequent changes in 

 deposition, while not always prolonged, appear at one 

 stage to have been of sufficient magnitude to allow the 

 accumulation of a large body of brackish water deposits, 

 the Belly River series. The surface so exposed was at 

 times covered by vegetation, and thin coal seams were 

 formed. This was subsequently covered by the marine 

 deposits of the Pierre stage of Cretaceous time. 



The close of the Cretaceous marine invasion is marked 

 by the brackish water beds containing the coal seams of the 

 Edmonton formation. During Tertiary time the deposits 

 were distributed in fresh water and this part of the contin- 

 ent was raised to sea level — the distribution bringing in land- 

 locked lakes or confined estuaries. The western Rocky 

 Mountain ridges probably did not bar drainage from the 

 gold bearing rocks of British Columbia, since the source 

 of the gold in northen Alberta streams is credited to the 

 lowest Tertiary or beds at the top of the Cretaceous. 



