GEOLOGICAL SURVEY OF THE TERRITORIES. 31 



greatest thickness adjacent to Fort Benton, near the source of the 

 Missouri Eiver. 



Formati6n No. 3 was named the Mobrara division, from the fact that 

 it is most conspicuous near the mouth of the Niobrara Eiver. These 

 three divisions constitute the lower series of Cretaceous rocks in the 

 West, and are supposed to be the equivalent of the Lower or Gray- 

 Chalk and Upper Greensand of British geologists. 



Formation No. 4 we call the Fort Pierre group, because it reaches its 

 greatest thickness near this post along the Missouri Eiver. 



Formation No. 5 was called the Fox Hills beds, from the fact that 

 they form a conspicuous range of hills between the Big Cheyenne and 

 Moreau Elvers. 



These two groups of rocks constitute the Upper Cretaceous series of 

 the West, and are regarded as the equivalent of the Upper or White 

 Chalk and the Maestricht beds of Europe. 



This brief description of the nomenclature of the Cretaceous rocks of 

 the West is considered necessary in this place, from the fact that I shall 

 be compelled to refer constantly to the various subdivisions in all my 

 future reports. 



The limestone rocks referred to as exposed on the high hills near the 

 Big Sandy, and upon the upper portions of the Big Blue and its tributa- 

 ries, belong to Cretaceous Formation No. 3, or the Niobrara division. 

 Formation No. 2, or the Fort Pierre group, I did not see exposed to view 

 in this region with certainty. 



The foundation of a saw-mill on the Little Blue, about four miles above 

 the junction of the Big Sandy, rests upon a dark pudding-stone, which 

 I suspect belongs to this group, but it cannot be of very great thickness. 

 About a mile above the mill, 50 or 60 feet of a dark gray calcareous 

 shale occur, holding a position beneath the true limestone, which I 

 suppose belongs to the Niobrara division, but which may possibly be in- 

 cluded in the Fort Benton group. I would remark just here that pale- 

 ontologically Formations Nos. 2 and 3 are embraced in one division, and 

 Formations 4 and 5 also, the fossils of one group of rocks passing up 

 into the other. 



As a general rule, all these formations are lithologically distinct. 



The soil of the valleys of the streams in Jefferson County is excellent, 

 and produces abundant crops. Some of the most productive and highly 

 cultivated farms which I observed in the State were seen in the valleys 

 of the Little and Big Blue Elvers and their tributaries. 



The belt of country underlaid by the sandstones of the Dakota group 

 runs northeast and southwest, extending through the States of Kansas 

 and Nebraska into Iowa and Minnesota, and is about 40 to 50 miles 

 wide. In this group there are about 45 to 50 feet of yellowish- white fri- 

 able sandstone, the small particles of quartz scarcely adhering together, 

 which I am confident will yet be made of great economic importance. 

 The sand, which is very abundant, could be used in plastering, in the 

 manufacture of bricks, and more especially in the construction of tlie 

 patent concrete which is so popular in some portions of this country and 

 Europe. 



The soil is largely composed of silica from this rock, and thus it seems 

 to be well adapted to the production of valuable crops of wheat, the 

 berry being more plump than that raised on any other geological forma- 

 tion in the State. 



On the more elevated prairie the soil is thinner, and we miss the 

 yellow-marl deposits which cover the first two tiers of counties along the 

 Missouri. Still the grass is short and nutritious, and the surface is dry 



