THE GEOLOGY OF NORTH DAKOTA 3 



in the Black Hills, but they are in this state deeply buried beneath 

 more recent formations. The Grafton well passed through, beneath 

 298 feet of drift and Lake Agassiz silt, 605 feet of Paleozoic strata, 

 including 288 feet of shale and sandstone, which has been referred 

 to the Cambrian, and 317 feet of limestone, sandstone, and shale, 

 which are believed to belong to the Ordovician.^ In the deep well 

 at Grand Forks, 40 miles south of Grafton, only one foot of lime- 

 stone was found just above the granite, showing a rapid thinning 

 of the formations in this direction, due either to inequality of 

 deposition or to erosion. The Ordovician appears to thicken 

 rapidly toward the north, for while at Grafton, as stated above, it 

 is 317 feet thick, 60 miles north at Rosenfeld, Manitoba, it has 

 increased to 700 feet, and is overlain by 192 feet of Silurian strata.^ 

 On the other hand, these formations thin out toward the west, and 

 at Morden, 2 7 miles from Rosenfeld and 1 5 miles north of the inter- 

 national boundary, the Ordovician and Silurian are absent, as 

 shown from the well record. The Dakota sandstone at Morden 

 rests directly on the Devonian beds. In the Morden well, at a 

 depth of 412 feet, 188 feet of Devonian red and gray shales and a 

 thin layer of porous limestone were penetrated, and strata of this 

 age cover a narrow strip of territory lying just west of the Silurian 

 in Manitoba. It is not unlikely that these Devonian and Silurian 

 strata extend south some distance into North Dakota. In the 

 deep well at the Jamestown asylum 19 feet of limestone was pene- 

 trated at the bottom of the wells, at a depth of 1,505 feet. The 

 well at LaMoure, about 40 miles southeast of Jamestown, struck a 

 compact gray crystalline limestone with a pinkish tinge at 1,300 

 feet, and went 28 feet in this rock, stopping at a depth of 1,328 feet. 

 The age of the limestone struck in these two wells is not known, 

 though it is probably to be referred to the early Paleozoic. During 

 the later Paleozoic the region does not appear to have been an area 

 of deposition and probably remained above the sea also throughout 

 a large part of the Mesozoic, since rocks belonging to the Triassic, 

 Jurassic, and Lower Cretaceous or Comanchean are, so far as 

 known, wanting in the state. 



' Ibid., p. 77. ^ G. M. Dawson, op. cit. 



