84 THE GLACIAL LAKE AGASSIZ. 



ment, and at Morden and Deloraiue/ varies in thickness from 128 to 545 

 feet. It comprises gray, principally calcareous shales, with "a band of 

 light-gray chalk, or mottled-gray chalk marl, about 200 feet in thickness, 

 outcropping along the foot of the Porcupine, Duck, and Riding mountains, 

 but lying below what is generally known as the Pembina escarpment on 

 the eastern face of the Pembina Mountain. * * * The Niobrara is 

 generally harder and more resistant than the terranes either above or below 

 it, and it often forms little abrupt cliffs in the midst of an otherwise gently 

 sloping country. It is, however, by the constant presence of great num- 

 bers of foraminifera that this terrane can be identified with the greatest ease 

 either in natural exposures or in the mud or small fragments of rock taken 

 from the wells bored with a percussion drill. These drillings, as a rule, 

 appear very uninviting to the geologist, but in the present case, when they 

 are carefully washed free from the impalpable clay that forms a large part 

 of their bulk, and examined under the microscope, they are found to deter- 

 mine the Niobrara horizon with almost as much aecm-acy as if good hand 

 specimens of the rock had been obtained."" 



In these borings the Fort Benton formation is represented lay a 

 stratum of gray shales, from 105 to 178 feet thick, underlain by the 

 Dakota sandstone, which had a thickness of only 19 feet on the Vermillion 

 River, and, with interbedded shales, was found to be 92 feet thick at 

 Morden, resting in both these wells on Devonian strata. Elsewhere in this 

 district, outcrops of the Dakota sandstone, and wells penetrating it, show 

 that its thickness ranges from .50 to 150 feet. 



The hracJiish- and fresJi-iratcr Laramie formation. — The marine Creta- 

 ceous strata of the Upper ]\Ii8souri country are overlain by the highest 

 member of this system, the Laramie formation, which was deposited in 

 brackish and fresh water. This series covers a broad belt in North Dakota 

 and IMontana, and stretches southward to Mexico and northwestward into 

 Assiniboia and Alberta. It is also well developed, but with interruptions, 

 along the Mackenzie to the Arctic Sea. The paleontologic characters 

 of the Laramie beds caused it to be long held in dispute whether they 



1 " Three Deep Wells in M.anitoba," Trans. Roy. Soc. Canada, Vol. IX, sec. 4, 1891, pp. 91-104. 

 = Trans. Roy. Soc. Canada, Vol. VIII, sec. 4, 1890, p. 113. 



