THE 
AMERICAN GEOLOGIST. 
Vol. XXX. JULY, 1902. No. i. 
ORIGIN OF ESKERS. 
By W. O. Crosby, Boston, Mass. 
Page, 
Introduction 1 
Evidence of existing glaciers and ice-sheets 2 
Characteristics of eskers 7 
Form 7 
Composition and structure 8 
Topographic and geologic relations 8 
Probable status of the ice-sheet during the formation of eskers 9 
Comparison of hypotheses ^ 17 
Superglacial hypothesis 19 
Subglacial hypothesis 22 
Review of evidence 24 
Direction or trend of eskers 24 
Length of eskers and eskcr systems 26 
Varying width of eskers 28 
Varying hight of eskers 29 
Branching of eskers 30 
Double and reticulated eskers 3t 
Topographic relations of eskers 32 
Relations of eskers to the ground moraine 33 
Relations of eskers to frontal and delta plains 35 
Composition and structure of eskers 35 
Sources of the material of which eskers and their terminal plains are 
formed 36- 
Introduction. 
The discussion of the orig-in of eskers seems to have sub- 
sided almost as completely as the glacial streams by which, it 
is universally conceded, they were formed. This is particular- 
ly true as regards the main question which glacialists have, 
in recent years sought to determine, — vis : Were subglacial or 
superglacial streams the principal factors in the making of 
eskers? A large majority of geologists are resting in the 
belief that these winding ridges of glacial gravel are the pro- 
duct chiefly if not wholly, of the subglacial drainage of the 
