844 
Culver—The Erosive Action of Ice. 
ice and the texture of the rock. If the rock be full of fissures 
and the glacier deep and heavy the rough hewing rules. If 
the rock be very hard and solid and the ice be not very thick, 
the planing will predominate over the rough-hewing and a 
gentle smooth billowy surface is the result. 
Although he does not say so directly, the inference is that 
Le Conte considers the rough-hewing to be efficacious in the 
making of rock basins. 
Prof. N. S. Shaler 5 accounts for the formation of rock basins 
with characteristic ingenuity. He says that owing to the ac¬ 
cumulation of the ice, the isogeothermal lines w.ill rise in the 
earth and will ultimately invade the lower part of the ice to 
such an extent that melting will ensue in the deepest portions. 
The water thus formed, being under great hydrostatic pressure 
will be forced out, thus deepening the basin and cutting down 
the rim where it escapes. He also thinks that as a result of 
this washing, the ice would slide toward the center of the basin 
thus increasing its size by wearing. 
To account for the basins in which this work goes on, Shaler 
supposes very slight original differences of level and very de¬ 
cided differences in the relative conductivity of the rocks, so 
that the isogeotherm of 32° would reach the ice in its ascent, 
not at a uniform level, but at points at different elevations. 
Contiguous ice masses, therefore, although lying at approxi¬ 
mately the same level would be differently affected. The base 
of one might be invaded by the melting temperature while the 
other remained free from such invasion. 
He applies this reasoning to the New England region to ac¬ 
count for the great number of lakes there. He regards it as 
more than probable that these lake basins have again and again 
been filled with ice, so that, as we now see them they represent 
the accumulated wearing of many glacial periods. 
Prof. T. C. Chamberlin 6 gives his view of ice action as fol¬ 
lows : 
‘The proper conception of its action as we view it, is that of 
a very stiff viscous liquid, into the base of which is incorpo¬ 
rated rocky fragments and earthy debris, which act upon the 
5 Proc. Bos. Soc. Nat. Hist., vol. 10, p. 358 et seq. 
6 Geology of Wis., vol. 1, p. 265. 
