38 The American Geologist. -Tuiy, ih92 
has been a source of perplexity to many geologists and earl}' led 
to a greatly exaggerated notion as to the amount of rock actually 
removed. Subsequent studies have shown that the pre-glacial to- 
pography remains with remarkable distinctness where not buried 
l)eneath glacial accumulations, and, consequently, that but little 
bed rock has been removed. Moreover, the case of the Hoosac 
mountains, described above, shows that in this place at least the 
original pre -glacially decomposed rock has not been all removed. 
If now it be assumed that in pre-glacial (or inter-glacial) times a 
considerable accumulation of secularly decayed rock existed upon 
the surface, the present accumulations may be accounted for 
without supposing a great deal of planing down of the rocks 
themselves. By this view the ice has acted more as a transporter 
of detritus already prepared than as a producer of such detritus. 
Moreover, this view of the glacial conditions also furnishes an 
explanation (in part at least) of that much discussed question of 
the origin of rock basins in glaciated regions. It yet remains to 
be proved that ice can, on a large scale, gouge out depressions. 
That under peculiar circumstances this is done is unquestioned, 
l)ut that all or even a large per cent, of rock basins are the re- 
sult of this action is not yet satisfactorily demonstrated. In a 
region of secular disintegration the rock surface would necessarily 
be irregular and one containing numerous basins where rock of 
an easily disintegrated nature exists. 
Pumpelly* suggests this point and accounts for similar basins 
in China by the action of wind in removing secularly decayed ma- 
terials. Chalmers,! speaking of the rock basins of New Bruns- 
wick, says: "These lake basins have evidently been formed by 
the sub-aerial decay of the rocks in situ in Pre-Quaternar}' times, 
the softer limestones, graphitic schists and ferruginous rocks 
having been more deeply acted upon than the gneisses and fel- 
sites." How far this idea can be extended by actual demonstra- 
tion is not at all certain for it has not been given the careful at- 
tention which it deserves. Secular deca}" undoubtedly produces 
just such forms, for it has regard chiefly for the chemical dura- 
bility of the rock. 
In their description of the driftless area+ Chamljcrlain and Sal- 
*Am. J. Sci., 1879, XVII, 133-144. 
tKept. Prog. Canada Geol. Survey, 1885, i, 17 GG. 
JSixth Ana. Kept. U. S. Geol. Survey, 249. 
