SURFACE GEOLOGY. 11 
later date, and the one by which the excavation of the lake basin was 
principally effected. 
Map showing directions of glacial strice along the margin of the highlands 
1, AL ATE ce a loli 
| ASHTABULA 
PORTAGE 
MAHONING 
The broad ice-sheets which have existed outside of Ohio have left 
their records in the nearly uniform and continuous glaciated surface 
which covers so much of Canada, New England, New York, and the 
States of the north-west. In nearly all parts of New England are traces 
of an ancient ice-sheet which moved in a direction about south south- 
east, and was of such thickness and magnitude as to override all the 
features of the local topography, except Mt. Washington. Hence the 
