Ori<iiii ffiuf A(je of the Lmi n-nl In n Lohis. — U/ihciii. 17H 
Warren is approxiiiiatel}^ indicated b}^ the accompanying map 
Fig. 1. Stages of the Ice Age in the United States and Canada. Unglacia- 
ted laud areas are dotted. 
(figure 1), which shows the maximum area of the continen- 
tal glacier and successive stages of its recession in the United 
States and southern ( 'anada. 
Lake Algo)iqiii)i. As soon as the glacial recession uncov- 
ered the Mohawk valley, the waters of lake AVarren. formerly 
outflowing at Chicago to the Mississippi river, were rapidly 
drawn away through the Mohawk and Hudson valleA^s. In 
the basins of lakes Michigan, Huron, and Superior, compris- 
ing the larger part of what had been lake Warren, there re- 
mained a similar but restricted body (tf water, which Spencer 
has named lake Algonquin, dammed by the lingering ice-sheet 
only on the part of its border east of (ieorgian bay, in the re- 
gion of lake Xipissing and the Mattawa river, and outflowing 
through the St. Clair river and lake, the Detroit river, and a 
stream which may be called the river Erie, continuing east- 
ward along the bed of lake Erie to the incipient Niagara river 
and falls. We shall return in a later part of this paper to 
further consideration of lake Algoncjuin and its ice barrier. 
L(tke Iroquois. In the basin of lake Ontario a glacial lake, 
ako much studied and named lake Iro(|Uois by Spencer, out- 
flowed at Kome, N. Y., to the Mohawk and Ihulson. Its sur- 
face at Toronto during the early part of its existence coin- 
cided nearly- with that of the jiresent lake Ontario: but later. 
