(', -if >!■',(( of Drift. — f)>/Hiu>. 379" 
ghi.cial or in the siil)<il;ici:il till, for it seems to \arv in this respect 
in (litt'erent districts. |)uriiii>- the progress of the accumulation of 
tlie suhglacial till, it was supplied mainly from the lower part of 
englacial material, in which l)oulders and fine drift of near origin 
Mere more abundant than higher \\\) in the ice. Hence, as a whole, 
doul>tless the subglacial till has more local material, though dif- 
fering little in tiiis respect from the basal part of the drift within 
the ice-sheet. The streams depositing kames and osars, as T be- 
lieve, brought these sediments largely from the upjjer and more 
j'en)otely di'rive(l portion of the englacial drift, and :dso ti'ans- 
ported them foi- t!ie greater j)art long distances, thus w»>aring the 
t)oulders and gravel to subangular and rounded forms. There- 
fore, in the order of their i)ei'centages of distances of transjjorta- 
tion. the subglacial till is generally lowest, and the englaeiid till 
next, while the stratified gi'avels. sands, and clays brought l»y 
streams from the ice were successively deposited, each mostly 
beyond the preceding and farther from their sources. 
I'crrlu'd I'tliH-Ls. When the ice-sheet was melted away, its en- 
closed ])Oulders were drop))ed. and some of them, lying as con- 
spicuous olijects upon the surface, are strown sparsely over the 
praii'ies or are perched, apparently where they might be easdy 
dislodged, on the slopes and crests of hills and mountains. Oc- 
casionally these perched blocks are of great size. Two found by 
Di'. (1. .^[. l>awson on the eastei'u foot -slope of the Kocky mount- 
ains, about IJ.IKMt feet a))o\(' the sea, nu'asure respectively 42 by 
4(1 liy 2<t feet and 4(1 by :;(l by 2(1 feet. Other blocks in the same 
region extend u}) to the height of r),2S() fiH't. and tliev all weiv 
dei'ived from the Arcluean area east and north of lake Winnipeg, 
some 7(M) miles distant.* 
I'resident ('haml»erlin has descrilxMl reinarkal)le iielts of abun- 
dant superficial lioulders associated with tei'Uiinal moraines in 
Illinois, linliaiia. and ()hio.t These l»ouldei's are almost exclu- 
sively crvslallinc .Vrcluean I'ocks. and ai'e thus known to have 
been transported across a distance of at least '!(l(l to .")(»(! miles 
from the i\orth. They show that here and tlicic in the ice-sheet 
rock masses, derived from remote hilly or niouiitainons tracts, 
were Itoriie foi'waivl high above the land: and that on the apinoxi- 
mately level country of thi'se states oidy tiic lower portion of the 
ice contained uiuch drift derived from local rook formations. 
*( Jeol. Survey of Canada, Ileport of Prosress for lsS2-S:!-84, pp. 147-14!) C 
tlJulletin, O; S. A., vol. 1, 1HI»0, pi.. >2T :!1. 
