[dowling] cretaceous SEA IN ALBERTA 35 



In Montana the widest extent of this early recession is marked by 

 the Eagle sandstones. The lower members are of marine and brack- 

 ish-water deposit. The middle is made up of sands and clays with 

 evidence of land plants and an occasional coal seam. Sands occur 

 again near the top covered by clays of brackish-water origin. Its 

 continuation westward, the Virgelle sandstone, is somewhat similar, 

 but has perhaps less evidence of fossils. In Alberta the castellated 

 rocks of Milk river occupy this horizon. The surface exposures of 

 the upper beds show signs of freshwater deposition. The base of 

 the formation on Rocky Spring plateau shows a gradation of heavy 

 sandstone beds with shale zones. These have not been carefully 

 examined for fossils but they rest on undoubted Benton shales. The 

 series in northern Montana possibly contain about 300 feet of beds. 

 The Cardium sandstones of the Bow River section are thin in com- 

 parison with the shore deposits of this horizon in the vicinity of the 

 Boundary line and are probably marine throughout. Their position 

 according to Cairnes^ is just above the Benton shales which here 

 seem to constitute the whole of the Colorado group. In the foothill 

 exposures north of the North Saskatchewan river the shore formations 

 of this horizon form the lower part of the Brazeau formation, including 

 probably about 200 feet of sandstones. We thus, in tracing this early 

 shore-line northward, arrive at the sandstones on the Peace river 

 named the Dunvegan sandstones. These show evidences of estuarine, 

 freshwater, and terrestrial conditions throughout, and resemble in 

 many particulars those of the Eagle and the castellated sandstones of 

 Montana and southern Alberta although they are of greater thickness 

 and have many more coal seams. 



These several examples of the early shore or delta deposits, if 

 the probable outline of the shore-line is considered, are found to con- 

 stitute two seaward projections, the building of which required the 

 transportation of a vast amount of material. The source of this 

 will naturally be from points up the land slope from each and suggests 

 two areas of recent elevation and denudation, one near the boundary 

 line, the other north of the Athabaska river. 



Lower Pierre (Belly River) Marine Deposits. 



The marine shales which form the base of the Pierre in the east, 

 here overlie the shore deposits, but do not continue far past the point 

 probably reached by the first inrush of the sea in the south. The 

 western extension seems to have been reached at Milk River ridge 

 and at the southwest corner of the Porcupine hills (see Plate V). 



1 Memoir 61, G. S. C. 



