Upham.] 
238 
[Feb. 18 , 
tion of the drift constitute a very important and significant part 
of the records of the Ice age, and suggest lines of observation and 
study to which little attention has been given. 
We come now to the last of the questions proposed for inves- 
tigation, relating to the proportion of subglacial drainage as com- 
pared with that which took place on the surface of the ice-sheet 
during its departure in the Champlain epoch. The glacial river- 
courses by which the modified drift enclosing these lakes and 
ponds was brought and laid down, being spread in plains close 
outside the retreating border of the ice-sheet, are shown by pro- 
longed ridges of irregularly bedded gravel and sand, which often 
extend in a series many miles, sometimes 20, 50 or even 100 miles 
or more in length. These ridges usually have steep sides and a 
narrow arched crest of variable height. Associated with them, 
and with the terminal and marginal moraines of the ice-sheet, are 
mounds, hillocks, and short ridges likewise composed of gravel 
and sand having a confused stratification, often somewhat anti- 
clinal in conformity with the slopes of the surface. Both the very 
long gravel ridges, or series of ridges, and the very short ridges, 
hillocks, and knolls, were formerly classed together, and were 
called kames, eskers, or osars ; but a useful discrimination has 
been proposed by McGee and Chamberlin, in accordance with 
which the term kames is now restricted to the gravel hillocks, 
knolls, and ridges of slight extent, while the long ridges are 
named osars or eskers. 1 Several osars often occur parallel with 
each other, or one alone may be traceable continuously a score of 
miles in a somewhat meandering and river-like course ; and two or 
more series of osars occasionally converge and unite like the 
branches of a river. They are admirably developed in New Eng- 
land and in southern Sweden, and have a frequent or at least a 
scanty representation in all glaciated regions. While generally 
regarded as the deposits of rivers draining the ice-sheet during its 
final melting, much diversity of opinion has been expressed con- 
cerning their precise mode of deposition, some observers believing 
1 W. J. McGee, in the Report of the International Geological Congress, second ses- 
sion, Boulogne, 1881, p. 621. T. C. Chamberlin, in the Third Annual Report of the 
U. S. Geological Survey, for 1881-82, p. 299; and Am. Jour, of Science, III, vol. xxvii, 
May, 1884, p. 389. President Chamberlin shows that the term osar (pi. osars), in this 
Anglicized form, has long been in common use by Jackson, Hitchcock, Desor, Mur- 
chison, and other writers. 
