324 ASSINNIBOINE AND SASKATCHEWAN EXPEDITION. 



water's edge, and is the prevailing formation from thence 

 to the foot of the Great Bend, where it passes by a gentle 

 dip beneath the water level of the Missouri. At Dorion's 

 Hills there is a fine section of this bed about eighty feet 

 exposed above the water's edge, containing its most 

 abundant and characteristic fossil, Ostrea congesta. In 

 many places, as opposite the mouth of Sunning Water, it 

 assumes the form of a long series of precipitous bluffs, 

 giving a pleasing variety to the general monotony of the 

 scenery. This is one of the principal characteristic ex- 

 ternal features of this formation. 



The upper portion of this rock is a yellowish and grey 

 calcareous marl, very soft and yielding, so that it is easily 

 cut up into numerous ravines by the temporary streams, 

 and thus the bluffs along this part of the Missouri often 

 present the appearance of a series of cones. The lower 

 stratum, however, is more compact, and forms a soft bluish 

 grey limestone. 



Though so well developed and covering so wide an 

 area, the middle and upper portions, at least, of this rock 

 can never be made useful for building purposes. Quite 

 soft and friable in places, when detached, it absorbs 

 moisture rapidly and crumbles in pieces. Being a rich 

 calcareous marl, it may be used at some future time as a 

 fertilizer. 



The fossils of this formation, though belonging to few 

 species, as far as is yet known, are numerous in indi- 

 viduals. A species of oyster {Ostrea congesta) is found in 

 great quantities throughout the bed, and in localities 

 Inoceramus problematicus is abundant. Fish remains, 

 though consisting mostly of scales and obscure fragments, 

 are disseminated throughout the deposit, several species 

 of which have already been identified and described by 

 Dr. Leidy. Entire thickness of this bed about 150 feet. 



