Englacial Drift. — Upham. 39 
the movement of its friction-hindered border is from the side 
of the valley into the ice mass. But the arched surface of 
tin- glacier and the great supply of its central current pre- 
vent the drift so worn off and borne away from being carried 
into the axial portion of the ice stream. Similarly the steady 
accession to the mass of the ice-sheet over any place by on- 
flow from its thicker central part and by the accumulating 
snowfall forbade the drift of the upwardly moving basal 
current from being carried far into the ice in comparison 
with its total thickness. The evidence of the esker called 
Bird's hill near Winnipeg, Manitoba, shows that much en- 
glacial drift had there been uplifted from a nearly level 
country to a hight of more than 500 feet in the ice-sheet.* 
Probably some of the englacial drift there was as high as 
1,000 feet or more in the ice, but doubtless a larger part was 
below than above the altitude of 500 feet; and this was on 
an area where the ice-sheet had attained probably a thickness 
of 5,000 or 6,000 feet, its lower fifth or sixth part bearing- 
considerable enclosed drift. In like manner the outer por- 
tions of the ice-sheet, where its thickness was less, had 
probably at its time of culmination no englacial drift above 
its lower sixth or fourth or third part. Whatever boulders 
and other drift became incorporated in the higher portion of 
the zone reached by the currents flowing upward would be 
thence carried forward in some regions, as from the Huronian 
and Laurentian areas north of lake Huron to the boulder 
belts in Illinois. Indiana, and Ohio, described by Chamberlin^ 
without intermixture with other englacial drift brought into 
the ice by less powerful currents on all the intervening 
extent, which in the case mentioned is about five bundled 
miles. 
Although the englacial drift is here spoken of as existing 
in large amount in the basal fifth or sixth pari of the ice- 
sheet, its proportion to the containing ire would yet be small, 
so that usually if a section could be inspected it would be 
*Geol. and Nat. Hist. Survey of Canada, Annual Report, new 6eries, 
vol. iv, for 1888-'89, pages 3G-42E. 
f'Boulder Belts distinguished from Boulder Trains— their Origin 
and Significance," Bulletin, G. S. A., vol. i, pp. "JT-.'U. "The Nature of 
the Englacial Drift of the Mississippi Basin.'' Journal of Geology, vol. 
i, pp. 47-60. 
