Glacial Geology in America, — Fairchild. 183 
as at present. This was an important observation and gave 
a basis for moderate views. In 1881 J. W. Spencer attributed 
the great lake basins to subaerial and fluviatile agencies, and 
professor Claypole the same. The complexity of their origin 
was emphasized by professor Chamberlin in 1883. and this 
now seems evident. 
In 1863 J. P. Lesley attributed the New York lakes, with 
Erie and Huron, to "northward rise of their flofjr-rock." This 
keen infererice has been verified by studies of the old shore- 
lines. It is now generally believed that the great lakes occupy 
preglacial basins of subaerial erosion, modified in some unim- 
portant degree by the mechanical abrasion of the ice; and that 
the ponding of the water, M'hile possibly due in some extent 
to morainal damming, is chiefly due to differential northeast- 
ward uplift. 
Dr. Newberry, as early as 1862, showed the existence of 
ancient river channels in the Erie basin buried under glacial 
debris, and proving the higher altitude of the land in pre- 
glacial time. In 1869 he predicated the existence of an un- 
discovered channel that must have been the preglacial con- 
nection of the Huron and Erie basins, and in many subse- 
quent writings he discussed the ancient drainage of North 
America. Dr. J. W. Spencer subsequently took up this work 
in the Laurentian basin with good results, and has endeavored 
to map the preglacial drainage of the great lakes. 
The studies of Spencer, Carll, Foshay. I. C. White, Salis- 
bury, Chamberlin, Leverett and others, indicate that some of 
the area, now drained southward by the upper Mississippi, 
Ohio and Susquehanna, was in preglacial time probably 
drained northward. 
Glacial Lakes. — The glacial phenomena receiving the lat- 
est serious study are those of ice-dammed water. The sub- 
ject has been found of unusual and romantic interest and con- 
siderable literature has accumulated, chiefly during the last 
decade. 
The necessary existence of lakelets or small ephemeral 
bodies of water between the ice foot and north-sloping land 
surfaces has long been recognized, but it is only in recent years 
that the conception has been enlarged to grasp lakes of vast 
•extent and duration. The possibility of such lakes has been 
