102 NEW YORK STATE MUSEUM 
The linear type of lake is by far the most common, this being pre- 
eminently true of the Finger lakes and to a large extent of the 
Adirondacks. It is well known that most of the larger lakes, espe- 
cially those of the linear type, occupy portions of preglacial stream 
channels. All the existing lakes are due, either directly or indi- 
rectly, to glacial action, and among the ways by which such bodies 
of water were formed.are these: by building dams of glacial drift 
across old river channels; by ice erosion; and by the filling of the 
numerous depressions which were formed by irregular deposition 
of the drift (kettle holes, etc.). Hundreds of small lakes, often 
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Fic. 34. The time of the Nipissing Great Lakes and Champlain submer- 
gence. The shaded area on the east was covered by sea water. 
After Taylor 
not more than mere ponds in size, belong to the last named type, 
while most of the large lakes are due chiefly to the existence of drift 
dams. 
Much has been written concerning the origin of the Finger lakes, 
and only the briefest summary will here be given. All are agreed 
that the lakes of this remarkable group occupy preglacial valleys, 
most of which, at least, contained north-flowing streams. These 
lakes have dams of glacial drift across their lower (north) ends, 
and the dams have largely contributed to the formation of the lakes, 
being in some cases perhaps the sole cause of the lakes. In the 
