PLATE LXI. 



CLAY COUNTY, 1888. WARREN UPHAM. 



About two-thirds of the area of this county were .covered by lake Agassiz, the 

 beach lines of which are very marked. East of the highest, or Herman, beach the 

 general surface at first falls away for a distance of say a quarter of a mile, but rises 

 then into a distinct rolling or undulating plateau of drift consisting essentially of 

 till. West of this beach, and more especially west of all the beaches, the surface is 

 almost flat, presenting an oceanic expanse over which distant objects rise first in 

 mirage, and later as ships at sea, with only their tops visible. This flatness continues 

 to and beyond the Red River of the North, which meanders in a very crooked course 

 northward in a narrow, shallow channel which it has excavated in the drift surface. 

 West of the beaches are no lakes, but east of them are numerous lakes like those of 

 the morainic regions of Becker county. Toward the north the Herman beach becomes 

 double, and still further north the other beaches are also doubled or tripled. 



In crossing this plain from the west to the east, two terrace-like elevations are 

 noticeable. One occurs at six miles east of Glyndon, running about north and south. 

 Here the ascent is about 200 feet in the distance of two or three miles. The other 

 terrace is that mentioned in connection with the Becker County plate (Plate LX), 

 and is especially distinct at White Earth Agency, about twelve miles east of the east 

 line of Clay county, rising about 300 feet still higher. These gigantic terraces are 

 supposed to be due to rock escarpments, now buried under the drift sheet, formed by 

 preglacial erosion. The western scarp is probably caused by a westward facing Creta- 

 ceous bluff, and the eastern, or highest, by a westward facing bluff of Paleozoic lime- 

 stone. The western (Cretaceous) bluff was probably much reduced and round^d over 

 by the operations of the glacial epoch; but the hight of the Paleozoic escarpment was 

 probably not so much diminished, and at the last one of the moraines of the region 

 was piled upon it through much of its course, giving it an apparent increase of hight. 



An interglacial forest bed has been found in the region of Barnesville, overlain 

 by twelve feet of till, the analogue of that found in Mitchell, Wilkin county. 



Along the immediate Red River valley the surface consists of stratified clay 

 which proves to be from sixty to ninety feet thick. This lies on the till and extends 

 right and left for several miles, no stones being visible on the surface. This clay is 

 supposed, by Mr. Upham, to be due to the river itself in its earlier history, when it 

 flooded considerable areas, rather than to lake Agassiz. Eastward from this allu- 

 vium the till rises to the surface, and stones appear. 



The till is also covered by sand and clay, apparently of the nature of delta 

 deposits, at Muskoda, brought into lake Agassiz by the Buffalo river at the time of the 



