374 REVIEWS 
those connected series of gravel ridges that are interpreted as the 
products of individual drainage systems of the ice sheet, the products 
of each river system being a gravel system. Some forty odd systems 
of this kind are recognized besides several less defined series and 
numerous branches and individual eskers, making on the whole a most 
phenomenal record of glacial drainage. The description of these 
occupies 170 pages. 
The classification of the gravels and associated deposits and a dis- 
cussion of their genesis follows and constitutes essentially the remain- 
der of the volume (chapters v and vi, 224 pages). The discussion 
of the genetic element is elaborate and detailed. Something of the 
range of special subjects may be gathered from the following special 
themes: Quantity of englacial débris; distinction between englacial 
and subglacial tills; the origin of drumlins; the relations of the 
marine gravels; bowlder fields and bowlder trains; single or multiple 
glaciation in Maine; the relation of the glacial waters to the glacial 
sediments ; the sizes of the glacial rivers of Maine; the zones of the 
Maine ice sheet ; englacial streams; the directions of subglacial and 
englacial streams under existing glaciers ; the internal temperatures 
of ice sheets; the basal waters of ice sheets; basal furrows as stream 
tunnels; the genesis and maintenance of subglacial and englacial 
channels ; the forms of glacial channels ; extraordinary enlargements 
of glacial river channels; the directions of glacial rivers compared 
with the flow of ice; the relations of glacial rivers to the relief forms 
of the land ; sedimentation in places favorable or unfavorable to the 
formation of crevasses; glacial potholes; the formation of kames 
and osars; the bowlders of the glacial gravels; comparative studies. 
on the glaciation of the Rocky Mountains and on the glaciers of 
Alaska; the modification of the glacial gravels by the sea; the short 
isolated osars or eskers; the hillside osars or eskers; the isolated 
kames or eskers ending in marine deltas; isolated osar-mounds not 
ending in marine deltas; the disconnected osars; the relations of 
glacial gravels to the fossiliferous marine beds; retreatal phenomena 
of the ice; causes of non-continuous sedimentation within the ice 
channels ; the continuous osars and their comparison with discontin- 
uous Osars ; were osars formed by subglacial or superglacial streams ? 
tests of subglacial and superglacial depositions; special features and 
their explanation. 
