306 THE GLACIAL LAKE AGASSIZ. 



This island lies in the course of northwestward and northward contin- 

 iiation of the Mesabi or eleventh moraine of the series mapped in Minnesota, 

 which next east from the narrows of Red Lake,rises A'ery prominently to a 

 height of 15<) to 200 feet for a distance of about 10 miles upon the penin- 

 sula dividing' tlie northern and southern parts of the lake. Like nearly the 

 entire western half or two-thirds of Minnesota, this whole region is deeply 

 drift-covered. No outcrops of the bed-rocks have yet been found on the 

 large portion of the Red River basin lying in Minnesota; but the conspic- 

 uous escarpment of Cretaceous shales, overspread by drift, along the west 

 border of the Red River Valley, wells penetrating to Cretaceous beds along 

 this great valley plain, and the topographic features of the land rising east- 

 ward from it with nearly the same rate of ascent as on the west, lead to the 

 belief that the eastern, like the western, border of this wide valley is formed 

 by an escai'pment of Cretaceous shales beneath the drift, and that the mod- 

 erately elevated area of Beltrami Island consists of these shales enveloped 

 by the glacial and modified drift. 



THE UPPER OR HERMAN BEACHES AKD DELTAS IN KORTH 



DAKOTA. 



FROM LAKE TRAVERSE NORTHWEST TO MILNOR. 



(PLATES XXIII AND XXVII.) 



From the southern extremity of Lake Agassiz, in section 18, Leon- 

 ardsville, Traverse County, Minn., the upper or Herman beach extends 

 northwestward 75 miles t(^ the most southern bend of the Sheyenne River, 

 in Ransom County, N. Dak., and thence its course is nearly due north, Ijut 

 with slight deflection westward, to the international boundary. The mouth 

 of Lake Agassiz was where now a slough 2 to 3 miles wide, with frequent 

 areas of open water, tributary to the Bois des Sioux River, stretches north- 

 ward from the northeast end of Lake Traverse. On the west side of this 

 slough and of Lake Traverse bluffs of till rise 100 to 12.5 feet; their tops 

 and the rolling surface of till which extends thence westward are 1,070 to 

 1,100 feet above the sea. 



The beginning of the upper or Herman shore-line west of the Bois 

 des Sioux is in the northeast corner of South Dakota, in sections 10, 3, and 



