VALLEY OF THE MINNESOTA RIVER. 581 



flowed through the old Blue Earth lake is doubtful. Rather 

 is it probable that the lake was formed earlier than lake 

 Agassiz and was bounded like lake Agassiz by the northern 

 ice sheet. 



Since the final recession of the ice from the valley of the 

 Minnesota fluvial action has been going on, building up 

 meadow land. Many of the lakes left by the glacial period 

 have either filled or have become much restricted in size. The 

 successive* generations of plants which have lived and decayed 

 upon the surface of the country have contributed to the soil 

 and this in varying extent has been redistributed by the action 

 of water and, very slightly, by the winds. The prairie has 

 been steadily encroaching on the forest and probably the 

 forest of today is much more limited in its extent over the 

 valley than formerly. Under the general forces at work, then, 

 the valley as it is seen to-day is the product of a long evolution 

 and it has reached its present characters of topography, as of 

 climate, geography, plant and animal population, by the con- 

 stant interworking of definite and, to some extent, calculable 

 forces. The impressive history of the river valley is, however, 

 to be matched with the equally impressive story of the varying 

 fortunes and the long struggle of its pi ant- inhabitants with 

 each other, and of the general conditions under which and 

 through which they have come to present the characters, dis- 

 tribution, prevalency and habits that are to be discovered in 

 them by the study of the modern flora. 



BIBLIOGRAPHY. 



Upham: The Minnesota Valley in the Ice-Age. Proc. Am. Assn. Adv. 

 Sci. vol. XXXII, pp. 213-231 (1883). 



Upham: Geology of Blue Earth Co., and other chapters, in Fin. Sep. 

 Minn. Geol. and Nat. Hist. Surv. vols. I and II (1884-1888). 



Hall: Physiographic conditions of Minnesota. Proc. Minn. Hort. Soc. 

 (1884), pp 391-405. 



Winchell: Geology of Hennepin Co., and other chapters in Fin. Rep. 

 Geol. and Nat. Hist. Surv. vols. I and II (1884-1888). 



Upham: Catalogue of the Flora of Minnesota. Ann. Rep. Geol. and 

 Nat. Hist. Surv. Minn, part VI (1884). 



Warrpn: Phys. Features of Minn. Valley. Rep. U. S. Chief Eng. pt. II. 

 Appx. (1874). 



Schott: Tables and Charts of Precipitation etc. Smith. Cont. Knowl. 

 vols. XVIII and XXII (1872-1882). 



Harmon, Payne, etal.: Rep. Minn, Weath. Serv. (1886-1891). 



Hall: Notable Dyke in the Minn. Valley. Proc. Am. Assn. Adv. Sci. 

 vol. XXXVIII (1889). 



