Review and Comment. 
357 
His explanation of the well known fact that a glacier often 
passes over till and even sand and gravel without removing it, 
is that the material is so soft and incoherent that the stones in 
the bottom of the ice would press into the yielding mass which 
would close up behind the on-moving stones and leave no result. 
In this simple way also he disposes of the theory that the 
lake basins were pre-glacial in origin and filled with the debris 
of weathering so that all the ice had to do was to sweep out 
this material. This, for the reason he has just given, it could 
not do. 
He quotes Dr. A Helland as stating that about 800,000 square 
miles of northern Europe is covered by Scandinavian drift to the 
depth of one hundred and fifty feet. As the area of the region 
from which it came is much less than the area covered, at least 
two hundred and fifty five feet must have been eroded from that 
region to supply the needed drift. 
Add to this what was lost by shipwreck in crossing the Bal¬ 
tic and North seas and what the streams have carried off since 
besides that which still remains in the lowlands of Scandinavia 
and we have, he thinks, as much as five hundred feet removed 
by the ice from Scandinavia during the glacial period. This 
supposed enormous erosion is offered in proof of the effective¬ 
ness of ice in such work. 
Without possessing any personal knowledge of drift phenom¬ 
ena in Europe the present writer still feels unwilling to ac¬ 
cept such figures as those just quoted. It is an established be¬ 
lief, if not an established fact, that here in America the drift of 
any region is from 75 per cent, to 90 per cent, local in origin. 
This statement refers to the newer drift. 
Considering crust movements to be the only alternative mode 
of the formation of lake basins, Mr. Wallace adopts the follow¬ 
ing criteria to discriminate between the two: Basins of erosion 
are characterized by, first, the absence of submerged ravines or 
side channels; second, the basin forms of the lake bottoms and 
the frequent occurrence ot two or more separate basins even in 
small lakes; third, the simple form of surface contour. He fur¬ 
ther notes that basins of erosion often have side valleys lying 
at higher levels than that of the main basin, the streams falling 
