WOEK I£J:rOETED I^^ THIS iIO^'OGl^APH. 7 



the glacial liver that was the outlet of Lake Ag-assiz was iiamcd Tiiver 

 Warren.* 



That this lake existed because of" the ban-ier of the receding ice-sheet 

 was first pointed out in 1872 by Prof N. H. \yinchell.* 



\\ OUK REPORTED IX THIS MOIfOGRAPII. 



Tlie part of the area of Lake Agassiz which lies in Minnesota, so far 

 as it is prairie, was explored by the writer in 1879 and 1881, under the 

 direction of Prof X. H. Winchell, State geologist; and in the latter j^ear 

 the highest or Herman beaches in that State, and small parts of lower 

 shore-lines, were carefulh- surveyed and mapped, their heights being 

 detennined by leveling, with the assistance of Horace V. Winchell as 

 rodman. Tliis work has been reported in publications of the Minnesota 

 Geological Sui-vey.^ It is also used in this raonogi'aph, wliicli comprises in 

 addition, for the part of the lake area in Minnesota, a large amount of later 

 obsei'\'ations made during my field work for the United States Geological 

 Survey, pertaining chiefly to tlie lower beaches, artesian wells in the Red 

 River Valley, and terminal moraines upon the region eastward to Red Lake, 

 Itasca and Leech lakes, and Brainerd. 



Exploration of the Lake Agassiz shore-lines, delta.s, and associated 

 glacial and lacustiine formations was again entered upon by the writer, 

 for the United States Geological Sm-vey, in 1885, as a part of the work of 

 the Glacial Division, under the direction of Prof T. C. Chamberlin. During 

 the years 1885 to 1887, inclusive, the upper or Herman beaches in North 

 Dakota, and extensive portions of the lower shores both in North Dakota 

 and ^linnesota, were mapped and their altitudes ascertained continuously 

 by leveling, in wliich I was assisted by Robert H. Young. We traveled 

 mostly afoot for this surveying, our daily advance vaiying from 3 to 10 



ered; depth of the bed rock," with maps; Report of Chief of Engineers, 1878, and Am. Jour. Sci. (3), 

 Vol. XVI, pp. 417-431, December, 1878. (General Warren died August 8, 1882.) 



'Proc. A. A. A. S., Vol. XXXII, for 1883. pp. 213-231; also in Am. Jour. Sci. (3), Vol. XXVII, 

 Jan. and Feb., 1884; and Geology of .Minnesota, Vol. I, p. 622. 



•Geol. and Xat. Hist. Survey of Miuncsota, I'irst Annual Report, for 1872, p. 63 ; and Sixth Annual 

 Report, for 1877, p. 31. Professor Winchell also explained in like manner the formeriy higher levels 

 of the Laurentian lakes, Poi)ular Science Monthly, .June and July, 1873; and the same view is stated 

 by Prof. J. S. Newberry in the Report of the Geological Survey of Ohio, Vol. II, 1874, pp. 6, 8, and 51. 



^Geol. and Xat. Hist. Survey of Minnesota, Eighth Annual Report, for 1879, pp. 84-87; Eleventh 

 Annual Report, for 1882, pp. 137-1.53. with map; and Final Kejiort, Vols. I and II. 



