and Deposits of Flooded Rivers. 41 



second Glacial epoch, showing that it was more prolonged and 

 complex there than eastward. Indeed, so definite subdivision 

 of the lacustrine history of the arid region, and its relationship 

 with the glaciers, living and extinct, of that region and of the 

 country thence north to Alaska, lead us to ask whether there 

 has not been a third as well as a second Glacial epoch, the last 

 affecting chiefly the far west and far north. 



Recession and final melting of the ice-sheet of the second 

 Glacial epoch from the Upper Mississippi basin, the Laurentian 

 lakes, and New England, took place only 7,000 to 10,000 

 years ago, according to estimates by Prof. N". H. Winchell, 

 from the rate of the postglacial erosion of the falls of Saint 

 Anthony ;* by Dr. Andrews, from the erosion of the bluffs 

 bordering Lake Michigan, and the resulting accumulation of 

 sand beaches and dunes about the south end of the lake ;+ by 

 Professor Wright, from the formation of valleys by streams 

 tributary to Lake Erie;:}; by Mr. Gilbert, from the Niagara 

 gorge and falls ;§ and by Professor Emerson, from alluvial 

 deposits of the Connecticut River. || The moraines stretching 

 from Nantucket and Cape Cod west to the Dakotas, Manitoba 

 and Assiniboia, are thus referred to a surprisingly late epoch, 

 almost verging upon the historic period of dawning civiliza- 

 tion in Egypt, China and India. The first great rise of Lakes 

 Bonneville and Lahontan was apparently contemporaneous 

 with the ice-sheet of the second Glacial epoch, which formed 

 these moraines, and with the maximum extension of glaciers 

 in the western Cordilleran region. After this there followed 

 a very dry climate in the far west, as shown by the Bonneville 

 and Lahontan sediments and shore-lines, corresponding doubt- 

 less to the time of departure of the last ice-sheet from the 

 northern United States and the greater part of Canada. 



The second rise of Lakes Bonneville and Lahontan belongs 

 to a later time when the far west again had a plentiful precipi- 

 tation, which was largely snowfall on the Sierra Nevada and 

 northward through British Columbia and Alaska, causing a 

 great development of glaciers and ice-sheets upon the Pacific 

 side of our continent. The date of this glaciation, whicb may 

 be called our third Glacial epoch, was, according to Russell, 

 " hundreds, but not thousands, of years ago."1~ It is probable 



* Geology of Minnesota, Fifth Annual Report, for 18*76; and Final Report, vol. 

 ii, 1888, pp. 313-341. Quart. Jour. Geol. Soc. London, vol. xxxiv, 1878, pp. 886- 

 901. 



f Transactions of the Chicago Academy of Sciences, vol. ii. 



% The Ice Age in North America, p. 466. 



§ Proceedings, Am. Assoc. Adv. Sci., vol. xxxv, for 1886, p. 222. "The His- 

 tory of the Niagara River," Sixth An. Rep. of Commissioners of the State Reser- 

 vation at Niagara, for 1889. pp. 61-84. 



| This Journal, III, vol. xxxiv, pp. 404-5, Nov., 1887. 



"f[ U. S. Geol. Survey, Monograph xi, Geological History of Lake Lahontan, p. 

 273. Bulletin, G. S. A., vol. i, p. 142. 



