Ci'lfi'riii nf]>r'ift. — J j>Ji(iiii. ''577 
fnictiun of the drift, or only a small amount, was coiitaiiuMl within 
the icc-.sheet. becomiiiu" siii>orol;ieial l>y ablation, at tiic time of 
its departure. 
EiKjJdcidl Till. The followinu- characters have seemed to me, 
iu examination of the (h'ift deposits of New Hampshire and other 
New England states, and of Minnesota. Iowa, the l)akotas. and 
Manitoba, to distinguish the englacial till, reaching from the sur- 
face to a A'ariable depth, as compared with the lowei' subglacial till. 
1. More plentiful and larger boulders are usually enclosed in 
the portion of the till that was englacial. Sometimes many of 
them are only partially embedded at the surface. 
2. These boulders and the smaller pieces of rock are mostly 
anguUir or subangular. While l>eing carried along in the ice- 
,sheet, the englacial drift was not subjected to attrition, which ac- 
counts for the large size aii<l unworn character of its rock frag- 
ments. 
)\. The englacial till has commonly a .somewhat more gravelly 
and sandy and less clave}' composition, owing to the washing away 
of much of its finer material by the drainage of the glacial meltiaig. 
4. Tt has a looser texture and is much more easily excavated 
This portion of the englacial drift was allowed to fall loosely when 
the ice disappeared. The subglacial till, on the (^>ther hand, be 
ing compressed by the vast weight <^)f the ice-sheet, l)ecame ver\' 
hard and compact, whence comes its popular name, •• liard pan.' 
."). The effect of weathering, by which the small ingredient of 
iron in the till has become changed next to the surface from i)ro- 
toxide comliinations to the hydrous sesquioxide. giving a'yellow- 
ish color, strongly in contrast with the darker gra}' and bluish 
color of the unweathered portion below, often is limited at the 
plane that .separates tlie readily permeable, loose englacial till 
from the comparatively impervious subglacial till. 
(i. 13etween the two, there is frequently a layer of sul)glacial 
stratified gravel and sand, from a few inches to a few feet thick. 
SuhyJtifkd I'lU. Characteristic features of till accumulated be- 
neath the ice are, conversely, the prevailingly smaller size and 
glaciated shapes of the enclosed l)oulders and fragments, its larger 
proportion of clay or very fine rock flour, its remarkable hardness, 
and in many sections the cessation at its top of the coloration dui- 
to weathering. 
Another criterion of sul)glacial lill i- the position of ils olilong 
