414 The American Geologist. June, 1897 
growing trees, proves that the ice border there is nearly or 
quite stagnunt. Russell, the explorer of that lee-sheet, has 
directed attention to the hindrance of glacial currents by in- 
closed drift.* It seems to me probable that this principle 
may explain the stagnation of the forest-covered ice in Alas- 
ka, and also a slackening or cessation of movement in the 
outer zone of the waning Pleistocene ice-sheets, to which the 
eskers of many districts appear to bear testimony. 
Effect of Superglacial Drift to diminish Ablation. 
It is further evident that the covering of drift on the outer 
part of the melting and receding ice-sheet yjrotected it in a 
degree from ablation by the sun's heat and by rains. On this 
outer zone of the ice, impeded in its movement by its contin- 
ued drift, melting was diminished, as compared with its ear- 
lier progress to the depth where it exposed the upper part of 
the drift; and as more of the englacial drift became super- 
glacial, the melting beneath proceeded yet more slowly. f This 
condition may have been true for a belt reaching back ten to 
twenty miles, or even, as I think, in some places fifty miles, 
from the extreme edge of the drift-covered ice, although in 
a decreasing degree the farther it extended. In other words, 
I believe that retardation of the ice movement by englacial 
drift, generally reached across the belt, of variable width, 
from one moraine to the next. 
Partly Contemporaneous Accumulation of 
Successive Moraines. 
While the border of the ice-sheet was sluggishly dissolving, 
strong glacial currents, favored by abundant snowfall and 
*lsi-ael C Russell, ''The Influence of Debris on the Flow of Glaciers," 
Journal of Geology, vol. in, pp, 823-832, Oct.-Nov., 1895. This admira- 
ble discussion and other helpful suggestions, relating to suptirglacial 
drift, given by J. B. Woodworth in the Am. Geologist, vol. xviii, pp. 
166, 167, Sept. 1896, have been the incentives of the study here present- 
ed. Prof. Russell's new book, "Glaciers of North America," first seen 
by me after this paper was written, treats (in pages 25-28 and 156-159, 
etc.) of the influence of inclosed and superglacial drift on the advance 
and retreat of ice-sheets. 
"fProf. N. H. Winchell, writing in the Popular Science Monthly for 
July, 1873, (vol. iii, p. 293, 294), held that the border of the waning 
North American ice-sheet was concealed under drift, nearly as the mar- 
gin of the Malaspina ice-sheet has been found by subsequent explora- 
tion. Compare my paper on "Englacial Drift," in the Am. Geologist 
for July, 1893, (vol. xii, pp. 36-43).' 
