THE IflOBRAKA EORMATIOX. 97 



But till or bowlder-clay, containing frequent granitic bowlders up to 5 or 

 sometimes 8 feet in diameter, thinly covers the shale, so that good expos- 

 ures of it are rarely seen, excepting in tlie bluffs cut by streams. 



In 'Western Manitoha and Assinihola. — Dr. George M. Dawson gives the 

 following summary of observations of the Cretaceous formations in the 

 district bordering the west side of Lake Agassiz nortli of the international 

 boundary, as obtained in the Geological Survey of Canada: 



The character and thickness of the diflferent members of the Cretaceous in the 

 Manitoba region liave 7iot been worked out in detail, owing to the extent of the drift 

 covering and scarcity of sections. * * * in the iiat country of the Red River 

 Valley no exposures of the Cretaceous rocks are found, and it is below the alluvium 

 of this region that the older subdivisions probably occur. The western margin of 

 the valley is formed by the escarpment of the second prairie steppe, and here, in the 

 so-called Pembina Mountain, and in its continuation to the northwestward, the 

 Cretaceous beds are tirst met with. About 25 miles north of the forty-ninth parallel, 

 where the Boyne River cuts through the Pembina escarpment, beds clearly referable 

 to the Niobrara group are known to occur, and precisely resemble, both lithologically 

 and in their included fossils, those of tlie corresponding Nebraska division. The roctk 

 is generally a cream-colored limestone, chiefly composed of shells of Inoceramus and 

 Ostrea congenta, but in places a white chalky material, which under the microscope is 

 resolved into a mass of foraminiferal shells, coccoliths, and allied nunute organisms. 

 This exposure, though probably small in extent, enables the outcrop of the Niobrara 

 to be defined at a point nearly 400 miles beyond the farthest northern locality known 

 previous to its discovery. Still farther north, along the outcrop of the Cretaceous, 

 at Swan River and Thunder Hill, west of Lake Winnipegosis, limestones and marls 

 containing fossils like those of the last-mentioned locality, and evidently of Niobrara 

 age, are again found, and other outcrops of these, and possibly of older beds, may 

 probably be discovered in this vicinity. 



With these exceptions, however, the Cretaceous rocks known to occur between 

 the Red River Valley and the Lignite group of the Souris region belong exclusively to 

 the Pierre group of the Cretaceous, while the Fox Hill group, which should intervene 

 between this and the lignite-bearing series, has not in this district been recognized, 

 and is, not improbably, but feebly developed. The Pierre rocks » * * consist of 

 dark-colored grayish, bluish, or blackish shales, generally homogeneous in character 

 through great thicknesses, and seldom containing fossils of any kind, though frequently 

 charged with selenite crystals and holding nodular layers of poor limestone. Expos- 

 ures of these beds are found in the Pembina escarpment on the Pembina River and 

 its tributaries, and on the Assiniboine, where the thick drift deposits have been cut 

 through. The clays or shales are generally quite characteristic in appearance, and 

 MON XXV 7 



