ALONG THE SHEYENXE EIVER. 91 



within 7 miles north and 20 miles southeast from Alta Vista, along the foot 

 of the steep eastern ascent of the Coteau des Prairies, at elevations from 

 1,150 to 1,250 feet above the sea. Perhaps some of these wells have 

 reached Cretaceous strata in place; but others evidently have been wholly 

 in the glacial drift, containing disrupted and transported masses of Creta- 

 ceous shale with fossils. The freouencv of these fossils in the drift indicates 

 that Upper Cretaceous marine strata originally covered much of this district 

 and supplied a large part of the drift, and that they probably underlie the 

 drift in the Coteau des Prairies. The list of fossils thus found includes 

 Bacitliff's ovatus Say, Placenticeras (Ammonites) placenta Dekay, both these 

 represented by abundant specimens, chiefly fragments; Scapliites nicoUetii 

 Morton, Nuciilu caiicelhifa M. & H., and an Iiioccramns which may be /. 

 prohle matte us Schlot.^ Twenty-five miles distant to the southwest and west 

 the crest of the Coteau des Prairies attains a height of 1,950 to 2,000 feet 

 above the sea, rising 800 feet above the outcrops and wells here noted. 

 This massive highland, beneath its mantle of drift, which probably varies 

 from 50 to 250 feet in thickness, doubtless consists mainly or wholly of the 

 Fort Pierre and Niobrara clays and shales, dipping very slightly to the 

 west and northwest. Because of the soft character of these beds, they are 

 not exposed in anv projecting knob or ridge; and their resemblance in 

 material and color to the bowlder-clay or till, which is derived in large part 

 from them, makes their exposures less liable to be noticed if they are 

 anywhere cut into by ravines. 



AloHf/ the Slieyennc Blrcr. — The Fort Pien-e shales have plentiful 

 exposures in the bluffs of the Sheyenne River, from where it flows by the 

 Cretaceous hills west and south of Devils and Stump lakes, covered partly 

 with morainic drift, as described in the next chapter, to the most southern 

 bend of this river, where it enters the area of Lake Agassiz. A sheet of 

 till, varying from 10 to 50 feet or more in thickness, sometimes with over- 

 lying beds of gravel and sand, forms the upper part of the Sheyenne bluff's, 

 and their lower portion consists of the dark-gray, easily disintegrating, 

 sandy shales of this formation to heights varying from 50 to 175 feet above 

 the river. There are many excellent sections of both the shales and the 



'Geol. and Nat. Hist. Survey of Minnesnt:!. Fiiinl Reyiort, Vol. I. 1884, ]i. 600. 



