POSTGLACIAL BIOTA OF THE GREAT LAKES REGION 117 



L. GLACIAL LAKE AGASSIZ (Plate XXXI) 



"A very important lake was also formed in the Red River Valley of the 

 North, discharging in its early history into the Minnesota River at Lake Tra- 

 verse. As Lake Agassiz was not connected with the complex system of basins 

 of the St. Lawrence Valley, it had a comparatively simple history. It grew 

 to the northward with the retreat of the ice which held it in at that end, and 

 continued to discharge into the Minnesota River at Lake Traverse, cutting 

 down its outlet and forming a series of breaches about its borders, until 

 the retreat of the ice enabled it to find a northerly outlet in some position yet 

 unknown. While discharging by this northerly outlet, it made another set of 

 beaches. On the further withdrawal of the ice, its waters were discharged, 

 and the lake became extinct. Lakes Winnipeg and Winnipegosis may be re- 

 garded as its diminutive successors in a sense, but they are rockbound lakes, 

 while Lake Agassiz was ice-bound on its northerly border." 8 Lake Agassiz 

 is believed to be contemporaneous with Lake Algonquin (vide Leverett) . 



Many lakes of greater or less size were formed at the borders of the Minne- 

 sota and Dakota lobes of the ice sheet. Lake Dakota, formed as the Dakota 

 lobe receded in South Dakota, is of interest in this connection, but no detailed 

 studies have been made of its old shore lines or life, if, indeed, there was 

 any life in its icy waters. 



III. Postglacial Sedimentary Deposits Containing Remains of Life 



Sedimentary deposits containing the remains of life have been observed 

 in many places. Some of these are referable to precise lake stages, but many 

 are in equivocable deposits and cannot be so classified. The data at hand, 

 old as well as new, are discussed by states, first considering those adjacent to 

 the Great Lakes and finally those from more remote regions; all are, however, 

 in territory once covered by the Wisconsin ice sheet. The modem nomencla- 

 ture is used for the lists of species. 



A. GREAT LAKES REGION 

 I. WISCONSIN 



References to postglacial lacustrine deposits from this state are apparently 

 rare, none being observed that record remains of life except those of Baker 9 , 

 Wagner, 10 and Goldthwait. 11 



• Chamberlin and Salisbury, Geology, III, p. 402. See also Upham, The Glacial Lake 

 Agassiz. 



» Joum. Cin. Soc. Nat., Hist., XLX, p. 175; Nautilus, XXVII, p. 68. 



111 Nautilus, XVIII, pp. 97-100. 



11 Abandoned Shore Lines, p. 61 ; Alden, Science, XXIX, p. 557. 



