12 



more than probable, as Hayden and Hall suppose, that it extends further 

 south to the sea. 



In tracing the eastern borders of the Dakota group, the length of its 

 area from north to south is recognized from the northern limits of the State 

 of Minnesota to North Texas, on about 20° of latitude. That this group ex- 

 tends farther north into British America maybe hypothetically admitted ; and 

 as the fossil leaves received from Greenland by Professor Heer, and consid- 

 ered by this author as Upper Cretaceous, represent some genera and, perhaps, 

 some species too, identical with those of the Dakota group, it would seem 

 that this formation has been continuous from the Gulf of Mexico to the 

 Arctic lands, Greenland, Melville, &c, over 35° of latitude. 



As far as it is known, in the States of Iowa, Kansas, and Nebraska, the 

 average width of the belt occupied by the Dakota group from east to west, 

 varies from sixty to one hundred miles. It has been seen that the red 

 sandstone of this formation is exposed in the southeast part of Guthrie 

 County, in Iowa, which is already ninety to one hundred miles east of De 

 Soto, on the Missouri River. In following up this river, the same formation 

 is still exposed to thirty miles above the mouth of the Big Sioux, where it 

 passes under the bed of the river. 1 This, in a direct line, is at least one 

 hundred and thirty miles. In Nebraska State, the width of the belt is, ac- 

 cording to Doctor Hayden, from sixty to eighty miles. 2 In Kansas I have 

 followed this formation along the Kansas Pacific Railroad, from the mouth of 

 Solomon River, for seventy-five miles to the west. Professor Mudge has col- 

 lected specimens of its fossil plants around Fort Larned, and recognized 

 the sandstone of the Dakota group, up the Arkansas River, to the limits 

 of the State. He says that the average breadth of this sandstone formation 

 in the northern half of the State is about forty miles, (northwest and south- 

 east,) or about sixty miles in a diagonal line running due east and west. But 

 when it reaches the bluffs of the Arkansas Valley the strike is westerly, and 

 instead of a westerly extension of sixty miles, it covers the whole country 

 from thirty miles east of Pawnee Rock to the western line of the State, a 

 distance of about two hundred miles. 3 It may be that it enlarges still far- 

 ther southwestward, for, according to Dr. Newberry's statement, it reaches 



1 P. V. Hayden's remarks on the Cretaceous rocks of the West. American Journal Science and 

 Arts, vol. xliii, p. 172. 



- Report, United States Geological Survey, (1867,) 2d edition, p. 52. 

 3 Transactions Kansas State Board of Agriculture, (1872,) p. 408. 



