

BOUNDARY OF THE GLACIATED AREA. 175 



drainage, which consisted of a broad, level-topped gravel 

 deposit from four hundred and iifty to five hundred feet 

 above the present bed of the Cheyenne River.* This old river- 

 bottom is about two miles wide, and, where we crossed it, 

 extended as far as the eye could reach both up and down the 

 valley. Subsequently Mr. Riggs found that it joined the 

 valley some miles above from the northwest. The gravel is 

 rather tine and well worn, and there is only an occasional 

 bowlder from one to two feet in diameter to be found upon 

 the surface. On the higher levels there are no traces of the 

 deposit. It has, therefore, as already said, the appearance of 

 marking a marginal line of drainage, which, north of the 

 Moreau River, was thirty or forty miles west of the Missouri, 

 but which joined the Cheyenne just west of Fox Ridge, and 

 followed that valley down to the vicinity of the Missouri, 

 and ever after kept near its trough till the river passed out of 

 the Territory at the Nebraska line. 



Soon after crossing the Northern Pacific Railroad in 

 Dakota, the glacial boundary turns abruptly to the west, 

 crossing the Yellowstone in Montana near G-lendive. We 

 give the delineation beyond this point in the words of Presi- 

 dent Chamberlin : 



" Passing north of the Judith Mountains, it again touches 

 the Missouri in western Montana, near the mouth of the Ju- 

 dith River, but at once swings away to the southward, to again 

 strike and cross the river forty miles above Fort Benton, and 

 about the same distance from the Rocky Mountains. Thence 

 it curves rapidly to the northward, crossing the national bound- 

 ary at the very foot-hills, and thence skirts them northward 

 to the limits of present determination. This is the outline 

 of the great northeastern sheet of drift. Along the Rocky 

 Mountains, within the United States, it barely comes in contact 

 with demonstrable glacial formations from the adjacent mount- 

 ains, though widely intermingled with mountain ' wash.' " f 



* The elevations are kindly furnished me by Rev. Thomas L. Riggs, of Oahe. 

 \ " Proceedings of the American Association for the Advancement of Sci- 

 ence," vol. xxxv, 1886, pp. 196, 197. 



