Classification ^ of Glacial Deposits, — Woodivortli. 8 1 
over which the ice-sheet moved, hence, superglacial, englacial. 
and subglacial categories of both stratified and imstratified 
drift. 
The criteria for the simpler determinations of the place 
held in relation to the ice naturally followed the recognition 
of the more general ear-marks by which it w^as shown that the 
drift was of glacial origin. The till associated with striated 
rock surfaces was first recognized as of glacial origin, while 
for a long time afterwards the water-laid drift continued to b-' 
regarded as some form of marine, or, at least, non-glacial de- 
posit. In fact, the glacial gravels and sands were so far sep- 
arated in theory from the influence of ice-sheets as to be de- 
nominated "modified drift," and the peculiar forms taken on 
in eskers and kames were attributed to the action of waves 
and currents in modifying the till during a time of submerg- 
ence of the. land. As yet it had not been seen that these 
water-worn deposits exhibit in their topography and arrange- 
ment evidence of the former presence of ice quite as convinc- 
ing as that arising from the association of striated rock sur- 
faces and fragments with the till group, evidence which we 
find in the kettle-holes and steep, often kame-like banks of 
ponds and terraces. 
The recognition and application of this evidence of the 
deposition of sands and gravels about or upon masses of ice. 
either the ice-sheet itself or outliers of it, have been slowlv 
brought about. It is difficult to say to whom the credit is 
due of first pointing out the evidence. The application was 
first made upon two groups of phenomena, the esker ridges, 
the kame-kettles and ponds; later.it was used in the diagnosis 
of the glacial sand-plains. N. H. Winchell, Upham, G. 
F. Wright, and perhaps the Scandinavian geologists ap- 
pear to have been the pioneers in regarding the water- 
laid deposits as reflecting the limits placed upon the 
distribution of the detritus b\' walls of ice. The prin- 
ciples first appear with a distinct enunciation in the 
writings of Gilbert* on the differentiation of the moraine ter- 
race, a geographic form in which slopes due to the deposition 
of debris by ice and water against the edge of a glacier were 
*Monograph i,, U. S. Geological Survey, 1890, pp. 81-83. 
