[dowling] cretaceous SEA IN ALBERTA 



41 



times considerable though periodically narrowed by the accumulation 

 of the sediments from the land and widened again by a slight sub- 

 sidence due probably to surface load. The period was of long duration 

 and allowed of the accumulation in this manner of about 700 feet of 

 sands and clays but also of many coal seams, several of which are of 

 great surface extent and thickness. This is especially true of the 

 coal-bearing zone marking the final deposits at the sea-level stage. 



The advance of the shore-line of the permanent land seemed to 

 have been slow through the whole period, as the thick measures period- 

 ically submerged extend well under the Paskapoo sandstones of the 

 Alberta syncline and thin out and almost disappear within the space 

 now covered by these Tertiary measures. 



In Saskatchewan the beds covering the marine deposits of the 

 Pierre are nearly all of freshwater deposition, so that they are more 

 likely to have been formed after the final retreat of the sea and to be 

 of later age than the brackish-water beds. 



The top of the Edmonton formation has been placed at a dis- 

 tinct coal horizon for convenience in mapping; but it appears to be also 

 very near the top of the brackish-water deposition of this period. 

 In southern Alberta there is no formation line drawn. The brackish- 

 water beds form the lower part of the St. Mary River formation. As 

 there is a very broad erosion valley between the exposures of these 

 formations and a possible eastern extension in the table land of the 

 Cypress hills a theoretical correlation is all that is attempted. The 

 marine Pierre shales are overlain in the Cypress hills by only about 

 150 feet of marine sands which are of varying thickness. These 

 although probably more nearly allied to the Fox Hills sandstones 

 are the extreme limits of sands of marine deposition and correspond 

 to the brackish-water beds to the west (Plate IX) and are covered by 

 continental deposits which could not be transported there until general 

 land conditions prevailed or until the Tertiary uplift. The correlation 

 of the Edmonton with these land-formed beds could not be made 

 but must be confined to beds beneath, that is, to the marine sandstones 

 and shales of the top of the Pierre. 



Eastward beneath the Tertiary beds of the Wood Mountain 

 plateau a thin deposit of brackish and freshwater material makes its 

 appearance (Plate X). It resembles the Tertiary beds, but the pres- 

 ence of remains of dinosaurs and turtles shows a proximity to the 

 sea. This formation attains considerable thickness in Dakota and 

 IS called the Lance formation. As it is of similar deposition to the 

 Edmonton it has been suggested that these two belong to the same 

 period and were probably connected deposits. Under the general 

 assumption that the Pierre sea retreated south and eastward, these 



