10 'tin American Geologist. July, 1893 
pronounced nearly free from drift. Even in the exceptional 
locality of Bird's hill, where I think we have evidence that 
thevolume of the ice-held drift was much larger than the 
average, being at least equal t<» a thickness of forty feet, it 
was distributed through probably 1,000 feet of ice, and per- 
haps no more than ten feet of drift was in the zone from 500 
up to 1.000 feet, so that the proportion of ice there to its 
drift would be as fifty to one. This consideration will 
mainly account for the impression received by observers of 
living glaciers and ice-sheets, that they contain very little 
englacial matter, which indeed is true as compared with the 
ice itself, though sufficient to produce an important part of 
its resulting drift formations. Again, it has often been 
remarked that icebergs show very scanty and rare enclosures 
of drift, but this is largely attributable to the submerged 
position of those parts, especially in the case of the tabular 
antarctic icebergs, which are melted away without over- 
turning. 
While favored districts, as near conspicuous marginal 
moraines and along belts of confluent ice currents, received 
sometimes not less than a thickness of forty feet of englacial 
drift, its usual amount on most other areas was probably no 
more than a few feet, perhaps seldom so much as ten feet 
and occasionally diminishing to almost nothing.* In many 
sections the englacial may be readily distinguished from the 
subglacial drift, and this is eminently true for the upper part 
of the englacial drift when it consists mostly of boulders 
transported long distances; but very frequently it is quite 
difficult or impossible to draw any line between the lower 
part of the englacial matter, which was principally of local 
derivation, and the accumulations of similar drift formed 
beneath the ice-sheet. j 
Englacial Drill heroines Super glacial only by Ablation. — 
Professor Chamberlin, in his recent very valuable paper on 
the englacial drift of the Mississippi basin, several times 
speaks of the opinions of writers who believe in the consider- 
able volume of the englacial drift, as if they suppose the 
""'Inequality of Distribution of the Englacial Drift, 7 ' Bulletin, G. S. 
A., vol. iii, 1892, pp. 134-148. 
f'Criteria of Englacial and Subglacial Drift," Am. Geologist, vol. 
viii, pp. 37G 385, Dec, 1891. 
