U. S. GEOLOGICAL SURVEY. 



MONOGRAPH XXXVIII PL I. 



T 



i and later drift sheets x'/.x 

 I Existing glaciers andice sheets 

 Quaternary lakes ( Bonn eville.Lahon tan and Glacial LakeA^assiz ) 

 \ Y\ Glacial currents known by strias 

 V\ V Glacial currents known by drift transportation or otherwise inferred 



Longitude We si 'jn c irom \>foelun.£-Lon 



MAP OF THE GLACIATED AREA OF NORTH AMERICA. 



(Modified from Upham's map Plate XVI Monograph XXV) 

 BY FRANK LEVERETT 



1898 

 Scale, about 550 miles to an inch 



