hor daring the Northern Pacific Railroad. 339 



much to say that every valley of the Park was once filled with 

 ice ; for moraines, bowlders, glacial lakes, and more rarely 

 glacial stria? give testimony on this question that cannot be 

 disputed. Ice-borne blocks are seen on the sides of the Yellow- 

 stone valley below the mouth of Gardner's Eiver, and south of 

 Mammoth Hot Springs every depression has once held a glacier. 

 Swan Lake is of glacial origin and is bounded on the south by 

 a terminal moraine, while lateral moraines and striated rook 

 surfaces mark the old ice level high up on the sides of the 

 valley. Near Marshall's the road leads over a succession of 

 great moraines of clay and bowlders which continue to and 

 around the Fire Hole basin, and prove that .this also was once 

 largely filled with ice. From all I could learn the evidences of 

 glacial action which are found here in the lowest portion of the 

 Park may be traced through all parts of it, 



DRIFT OF THE UPPER MISSOURI. 



The Missouri River, formed at Gallatin City by the union of 

 the Madison, the Gallatin and the Jefferson, traverses with a 

 northwest and then northerty course the valley between the 

 Eocky and Belt Mountains, and finds its way out to the plains 

 by a long circuit around the northern bases of the Belt and 

 Crazy Mountains, eastern outliers of the Rocky Mountain sys- 

 tem. Cutting through barriers formed by interlocking spurs 

 at the "Gate of the Mountains," the river enters an undulating 

 prairie country which extends from the north side of the Belt 

 Mountains to and beyond the Canadian line. All this region is 

 occupied by a sheet of drift that in thickness and extent rivals 

 that of the plains surrounding the Canadian highlands; but, as 

 far as my observation extended, I found this of local origin. 



At the Great Falls of the Missouri the underlying rock is 

 exposed, but the drift-sheet comes up to the edge of the gorge 

 and forms the low hills which stretch away to the east and 

 north like the long swells of the ocean. In the valleys of the 

 streams which come down to the Missouri from the Belt Moun- 

 tains, the rock substratum is generally visible ; but the interven- 

 ing plateaus are covered with a sheet of drift that varies greatly 

 in thickness as it is spread over a rock surface that was once 

 deeply and irregularly eroded. For example, near the Upper 

 Falls of the Missouri, where the banks of the river are solid 

 rock and perhaps a hundred feet high, a tributary coming in 

 from the south cuts across an old valley filled with drift, which 

 extends almost to the present river channel. At its mouth 

 this tributary has high rocky banks, but a few hundred yards 

 above they are altogether composed of drift. This is a true till, 

 thickly st:t with bowlders, some of which are two feet or more 

 in diameter. 



