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 actidn 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 along 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 plant-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. Rep. 
Minn. Geol. and Nat. Hist. Surv. vols. I and IT (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. 
Gevl. and Nat. Hist. Surv. vols. I and I1 (1884-1888). 
Upham: Catalogue of the Flora of Minnesota. Ann. Rep. Geol. and 
Nat. Hist. Surv. Minn. part VI (1884). 
Warren: Phys. Features of Minn. Valley. Rep. U. S. Chief Eng. pt. II. 
Appa. (1874). 
Schott: Tables and Charts of Precipitation etc. Smith. Cont. Knowl. 
vols. X VIIL and X NII (1872-1882). 
Harmon, Payne, etal.: Rep. Minn. Weath. Serv. (1886-1891). 
Hall: Notable Dyke in the Minn. Valley. Proc. Am. Assn. Adv. Sci. 
vol. XXX VIII (1889). 
