206 DHE JOORNAE VORP NG EOLOGN: 
freedom upon a plain of moderate undulation. It is therefore a 
matter of much good fortune to find a portion of Greenland upon 
which the glaciers are now deploying with something of the 
freedom that the Pleistocene glaciers enjoyed upon the main- 
land. The outward movement of the ice upon the plateau sur- 
face of the Inglefield Gulf region is scarcely less free than upon 
the average surface of the mainland field. It is, I think, on the 
whole, more free than the ancient deployment was upon the 
average surface of New England and the Middle states, though 
somewhat less free than that upon the average plains of the 
upper Mississippi and of the great interior of Canada. The 
interruptions of the movement at the border of the ice consisted 
almost solely of the effects of the valleys that led down to the 
Gulf. Into these a portion of the border of the ice sheet crept 
and stretched forward in tongues from one to three miles long, 
or in the greater valleys at the heac of the bays, a few miles 
longer. In about half these cases the glacial tongues reached 
the sea level. Inthe remainder, they stopped short by distances 
ranging from a few rods to two or three miles. 
The geological structure of Greenland is in general unfavor- 
able to glacial studies. The prevalence of any single formation 
in a glacial region is infelicitous, because it fails to furnish data 
for determining the precise locality from which given bowlders 
have been derived, and hence for ascertaining the courses they 
have pursued, the rate of wear, and other vital elements of their 
history. It is especially unfortunate when the formation is one 
so versatile and deficient of order as the great crystalline com- 
plex of Greenland. There is in this case the added misfortune 
that the débris is chiefly coarse and arenaceous, and hence that 
characteristic admixture of clay and bowlders which constitutes 
till, the most typical glacial formation, is generally absent. Not 
only are the conditions of identification unfavorable, but the 
conditions for production are adverse. 
In the Inglefield Gulf region, however, there is considerable 
relief from these untoward features. The clastic series contains 
enough of material reducible to a fine silt to give, under suitable 
