420 THE GLACIAL LAKE AGASSIZ. 



are till (fig. 18). At Mountain this shore descends 30 feet, from 1,045 to 

 1,015 feet, within a distance of about 25 rods. It is wholly till, with 

 no associated beach formation, as also are the more gentle slojjes on 

 both sides, sinking toward the east and rising westward. During all the 

 Campbell stages of Lake Agassiz erosion was in progress upon this long 

 escarpment; but in some localities the action of the waves in cutting away 

 and removing the till was temporarily changed, alternating with accumula- 

 tion of shore deposits of wave-brought gravel and sand. 



Erosion of the base of the "first Pembina Mountain" — that is, the front 

 of the Pembina deltn, along a distance of 6 miles to the southeast from 

 Walhalla — supplied an extraordinarily massive Campbell beach or embank- 

 ment, varying from a quarter of a mile to nearly 1 mile in width, which 

 extends 8 or 9 miles in a curving com-se, convex to the southeast, through 

 sections 5, 8, 17, 20, 29, and 30, township 161, range 55, and the south half 



Fia, 18 Profile of the Campbell eacarpment 1 mile south of Mountain. Scale, 100 feet to an inch. 



of section 25, the southeast quarter of section 26, and the west half of sec- 

 tion 35, township 161, range 56. This broad belt consists of gi-avel and 

 sand, 15 to 40 feet or more in depth, wliich were carried southward by the 

 shore currents of Lake Agassiz in its Campbell stages, the greater ])ortiou 

 being transported 6 to 12 or 15 miles. A section crossing this deposit is 

 shown in fig. 19. The crest or somewhat plateau-like top of the embank- 

 ment in its course of 6 miles south of the Tongue River has an elevation 

 of 1,020 to 1,030 feet above the sea. In its narrower part, north of this 

 river, its crest ranges from 1,028 to 1,033 feet along the first mile from 

 the river; 1,030 to 1,035 feet along the next mile; and 1,035 to 1,045 feet, 

 averaging 1,040 feet, in its third and most northern mile, passing through 

 the southwest edge of section 29, township 162, range 55, where it becomes 

 an ordinary beach ridge only 20 to 30 rods wide, with descent of 15 feet 

 to the east and 5 feet to the west. The process of accumulation of the 



