1S4 The American GeoloejiM. Marcii, 1893 
numorous inulevelopod joints for a time lie in 11 position where 
they m:iv be att'ected by decay the incipient fractnre phmes are 
thereafter easily opened by n rehitively slight strain. Sucli a 
stress applied to the pebbles which now lie in our modified drift 
Avill often lead to the chipping of the stones. There is much evi- 
dence going to show frequent advances and r(H'essions of the 
glacier during the last ice period ; each of the pauses of the on- 
going would be likely to give a chance for the process of decay to 
take effect. In the next advance of the ice one can readily believe 
that the movement developed the incipient fractures and polished 
the new made facets by the friction ))rought al)Out in the moving 
mass of pebbles and sand. 
T do not intend to say that all the artificial looking stones Avhich 
liave been found in our earlier drift deposits have been formed 
in a purely natural way, yet I am prepared to affirm that at least 
one enquirer who has tried to approach the matter in a dispassionate 
manner has found it necessary to guard himself in a careful manner 
from self deception as well as against the devices of others. It 
is clear that there are perfectly natural processes by which pebbles 
ma}- be chipped in such a manner that now and then one of them 
may have a very artificial aspect. Finding unquestionable stone 
implements on the surface or at shallow depths, within the cul- 
ture layer, it is natural to suppose that the lower lying chipped 
pebbles are ruder specimens of the same general nature. It is 
clear that just here we have a pitfall most dangerous for the un- 
wary. 
Or.DKK I)kikt in the Dkn.vwark A'allkv. 
A. A, W'rkjiit, Oberlin, Oliio 
80 large a question as the unity or duality of the glacial epoch 
must necessarily rest upon a great variety of considerations. The 
onlv point to which reference will here be made is the question of 
the existence of a distinctly older drift in the Delaware valley, a 
region which I have examined with some care, and concerning 
which I will offer onl}' the briefest summary statements. 
It is stated in the geological report of New Jersey for ISHl that 
glacial deposits exist far south of the "terminal moraim;" of the 
"second"' glacial epoch, which crosses the Delaware river at Bel- 
videre : that these deposits cannot be considered as the attenuated 
