187 
perhaps entirely disappeared. The waning of the ice probably 
required a somewhat longer time than did its formation and 
growth. 
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Ire. 15. Map of maximum glaciation of North America. The white spot 
in Wisconsin is a “ driftless area,’ never covered by glaciers. Solid black 
areas are mountains covered by local glaciers. (After Lawrence Martin. 
Irom Pirsson & Schubert, A Text-Book of Geology. Part II, p. 651.) 
(6930) 
First Interglacial Epoch 
— 
Now followed an epoch with climatic conditions much as today, 
an Interglacial Epoch, so called because of its occurrence between 
two glacial stages; for at length the temperature again fell and 
the snowfall increased, ushering in a second glaciation. 
