PREFACE 



In my work for the Geological and Natural History Survey of Minne- 

 sota, from 1879 to 1885, under the direction of Prof. N. H. Winchell, State 

 geologist, the highest shore-line of Lake Agassiz in that State was mapped 

 through its prairie portion, extending about 175 miles from Lake Tra\'erse 

 eastward to Herman and thence northward to Maple Lake. During this 

 survey Mr. Horace V. Winchell was my efficient assistant as rodmau in 

 leveling. The exploration showed that a very large lake occupied the Red 

 River Valley in the closing stage of the Glacial period, when the ice-sheet 

 was being melted away from this district. Terminal moraines of the ice- 

 sheet, forming a series of eleven in consecutive order from south to north, 

 were also explored and mapped in Minnesota; and it was seen that the 

 glacial lake and moraines were intimately related as records of the recession 

 of the ice and the transition from the Pleistocene to the Recent or present 

 geologic pei'iod. 



It became e^^dent, however, that a satisfactory investigation of the 

 extent and history of Lake Agassiz must comprise both sides of the Red 

 River Valley. The United States Geological Survey therefore undertook 

 the more extended examination of this lake area, which was assigned to 

 me, as a member of the Glacial Division, under the direction of Prof. T. C. 

 Chamberlin, for whose friendly counsel and constant interest in this work I 

 huxe the pleasure of recording here my great indebtedness. Suggestions 

 derived from the previous work for this Survey by Mr. G. K. Gilbert and 

 Mr. I. C. Russell on other Pleistocene lakes also aided me much in both the 

 field work and the study for prepanng this report. 



Again, when the shore-lines of Lake Agassiz had been mapped through 

 North Dakota from Lake Traverse to the international boundary, it was 

 found that a comprehensive monograph of this subject could not be pre- 

 sented while the exploration was restricted by a political limit. Hence it 



