PLATE L. 



WILKIN AND TRAVERSE COUNTIES, 1888. WARREN UPHAM. 



These counties are wholly without exposures of the underlying rock, and the 

 drift surface is monotonous. Within the area of glacial lake Agassiz the surface is 

 flat or so nearly flat that it is only at long distances that any change of altitude can 

 be detected. Outside of the beaches of lake Agassiz the surface is but little more 

 undulating. Into this very uniform prairie surface the main streams have excavated 

 sharply bluff-lined valleys. These are the Red River of the North and the Bois des 

 Sioux, with its southern extension to lake Traverse, whose bluffs are from twenty to 

 forty feet high. The bluffs along lake Traverse, on each side, are composed, so far 

 as known, of till, and rise from 100 to 150 feet above the lake, being highest along 

 the southwest part of the lake. These continue on each side of Brown's valley to 

 Big Stone lake, having about the same hight; thus there is plainly an ancient water- 

 course, once occupied by a large river, connecting the valley of the Bois des Sioux 

 with the valley of the Minnesota. This valley was the way of discharge of lake 

 Agassiz until, by the retreat of the glacier, it found a lower outlet toward the north. 



The beaches of lake Agassiz consist of gravel and sand in the form of continu- 

 ous, smoothly-rounded ridges, rising from three to ten feet above the land on the 

 east, and from ten to twenty feet above that on the west. These beaches vary from 

 ten to twenty-five or thirty rods in width, constituting broad, wave-like swells with 

 a smooth, gracefully-rounded surface. They are but seldom interrupted by unfavor- 

 able conformation of the original shore line, or by subsequent removal by streams, 

 and hav been traced continuously for a distance of 175 miles in the state of Minne- 

 sota. They also exist in Dakota, and run into Manitoba. These beaches, in descend- 

 ing order, have been named Herman, Norcross, Campbell and McCauleyville. The 

 till on which they lie is usually of the ordinary kind, but occasionally shows strati- 

 fication. This till furnished the gravelly material of the beaches under the action 

 of waves. It also supplied that of some stratified clay which sank in the deeper part 

 of the lake. Such clay, however, is not widely spread, but is confined essentially to 

 the central depression of the Red River valley. This restriction of these clays seems 

 to show, according to Mr. Upham, that they originated, not during the existence of 

 lake Agassiz, but at a later extended fluvial epoch by streams that flooded the valley 

 with muddy water, carrying occasional vegetation. 



The Herman beach is eighty feet above lake Traverse. 



The Norcross beach is twenty-five feet lower. 



The Campbell beach is fifty feet still lower. 



The McCauleyville beach is ten feet lower than lake Traverse. 



