/// '///'/ lint, i nit Of Y(W '' in I '.' 1 1, 



fains, tin- rock substructure is visible: hut tin- int- 

 plateaus are covered with a sheet of drift clay and boulo 

 that varies greatly in thickness, as it is spread over a rock-sur- 

 face that was once deeply and irregularly eroded. For example, 

 near the Upper Falls of the Missouri, where the banks of the 

 river are perhaps a hundred feet high, of solid rock, a trihutarx 

 coinini: in from the south cuts across an old valley tilled with 

 drift which extends almost to the promt river channel. A 

 mouth, this tributary has hi^h rocky banks : but a few hundred 

 yards above, they are altogether composed of drift. This drift 

 is a true till, thickly set with boulders, some of which are two 

 feet or more in diameter. They are usually rounded, somet 

 subangular, and are composed of gray or red granite, quart /He. 

 palaeozoic limestone, and a variety of eruptive rocks. Th. 

 semblance of this drift to that from the Canadian highlands, is 

 so great that I was only convinced of its local origin when I 

 found all of its constituents in place in the Kelt and Kock\ 

 Mountains. The granites were to my eye indistinguishable from 

 those of the eastern Laurentian series ; they are of An-ha-an a-e. 

 as I subsequently learned ; and nothing but careful microscopic 

 examination will show them to be distinguishable, if they are so. 

 These facts lead me to suspect that even the very careful and 

 experienced observers who have reported the finding of east tin 

 Laurentian boulders on the flanks of the Rocky M>n 

 feet above the sea, may have been misled by this striking resem- 

 blance. 



On the undulating surface of the table-lauds between the tribu- 

 taries of the Missouri, large boulders are occasionally seen, a 

 the States bordering the Great Lakes ; and one of thes- 

 wliat angular in form, has served so long as a rubbing-pout for 

 the buffaloes which recently abounded in that region, tlur 

 sides are all polished and a deep furrow is worn around it. 



Immediately south of the Falls of the Missouri, an extensive 

 coal-basin of Cretaceous (?) age is opened b\ the \ the 



Oil which come down from the Kelt and Ih-hwood Mount- 

 ains. Two coal seams are exposed, one thin. fmm ]-.' 

 to is feet in thickness, the latter a compound soaro, some of tin- 

 benches of which are bright, pure coking coal. 



The Falls of the Missouri, caused by beds of sandstones b 



