The Origin of Drvmlins, — Tarr. 405 
Rivers for a similar reason meander through their flood- 
plains in a series of beautiful curves changing in form and 
position. Ice is commonly compared to rivers in its modes of 
action, and this has been done even in connection with this 
very subject of drumlin formation; and now I ask. may not 
ice have the same habit as meandering rivers? If this be so. 
drumlin s are an expression of the alternating, rhythmic eros- 
ion curve — they are the boundaries of the ox-bow curves of 
the ice stream. 
This much for the general subject; we have even less that 
is explicit for the details of the process. But a moraine 
overridden by the ice would certainly be subjected to marked 
changes, and these, as the writer conceives them, are somewhat 
as follows. The surface portion would be ground finer, and, 
if stratified at the beginning, might have its stratification des- 
troyed and its sandy structure changed to true till by the 
grinding action of the ice. It would at the same time become 
more compact. This material, added to the ground moraine 
deposited by the retreating ice, might well leave a coating of 
true till with a depth of fifteen or even thirty feet, so that, un- 
less cut deeply, the original stratification would not appear in 
the drumlin. This is certainly the condition indicated at 
Gardner, Massachusetts, and may well be suspected in other 
drumlins. 
It is not the author's intention to insist that this theory i- 
a true explanation, much less that it is the only explanation; 
hut. rather, to urge that it be not too easily put to one side. 
As investigations proceed, new facts will be discovered, and 
it is Safe to predict that eventually the true explanation of 
drumlins will be found. In the meantime, if this theory does 
furnish the real explanation, the proof of it will be more easily 
and more quickly discovered if investigators bear in mind that 
it is by no means a disproved theory, as some students of gla- 
cial geology seem to assume. 
This can certainly be claimed for the theory: that it is not 
impossible, and that no vital objections have been urged 
against it; but that, on the contrary, it is the only theory 
that has more than mere hypothesis to support it. Rock hills 
of drumlinoid outline are thus carved by ice erosion; and. if 
this be true of rock, why may it not also he true id' incoherent 
