42 Bulletin Wisconsin Natural History Society [Vol. 12, Nos. 1 & 2 
many cases they are not even congeneric with present arctic ani- 
mals. Yet by the same method of reasoning we could argue that 
today an arctic climate exists in Louisiana, Mexico, Central Amer- 
ica, or even southern India! To cite a few examples of present dis- 
tribution, the muskrat is found congeneric {Ondatra) from southern 
Louisiana to the Arctic Ocean and conspecific {Ondatra zibethica) 
from northern Georgia and southwestern Texas to the Arctic 
Fig. 9. Outline Map of the Middle Portion of North America, 
Showing the Location of Ridgeway Bog (B) and the Southern 
Margin of the Wisconsin Drift (indicated by heavy line). 
Ocean; the mink is found conspecific {Mustela vison) from southern 
Louisiana to northern Alaska; the otter is congeneric {Lutra) 
from Central America to northern Alaska, and the beaver {Castor) 
occurs from extreme southern Texas to northern Alaska. Nor 
are mammals having a great north and south range confined among 
aquatic or semi-aquatic ones: the wolf ranges from almost tropical 
southern Florida to the mouth of the Mackenzie River; the weasel 
is found from Brazil to the Arctic Ocean; the mountain sheep from 
