Feb., 1907.] 
The Columbus Esker. 
6 5 
application conforms to the restriction placed upon the term by 
Stone, for these gravel ridges are, as a whole, both short and in¬ 
terrupted. 
Chamberlin and Salisbury ( 7 ) in their recent work, use osar 
or esker and kame in the same sense that Chamberlin used them 
in “The Great Ice Age” mentioned above. The limits of the 
terms are perhaps a little more sharply drawn. 
Thus we see that at the beginning in Sweden the term osar 
was applied to these gravel ridges. Ireland developed the term 
esker for them while in Scotland they were called kames. Later 
these terms were used interchangably for these formations in 
other parts of the world. Still later Geikie in Scotland and 
Chamberlin in America restricted the term kame to those gravel 
bunches and ridges which stood in more or less close relation to 
the terminal moraines and applied osar or esker to the others, 
i. e., those parallel with the flow of the ice tongue. More re¬ 
cently Stone limits esker to short interrupted osar while esker 
alone is employed by Leverett in his works. Because of these 
well defined usages, osar or esker on the one hand and kames on 
the other should not now be used interchangeably. It would, 
perhaps, have been better also to have differentiated between 
osar and esker as used by Stone, in the second best developed 
field in the world, but Geologists in subsequent papers have not 
accepted this latter distinction. 
General on Eskers. 
The place best fitted for the development of osars and eskers 
seems to have been a zone just within the periphery of the ice- 
sheet, at its maximum extension or at its subsequent stages of 
retreat. They may rest upon the bed rock or upon till stratified 
or unstratified. As before stated, they follow more or less eloselv 
the direction of the ice-flow as shown by the striae on the bed 
rock. They quite often follow the valleys of their region, but 
striking exceptions to this occur. Xot infrequently they extend 
from a stream valley up and across a low divide of 200 feet 
(sometimes 400 feet) and down again into a valley on the other 
side. Instances are recorded where they cross a lake, their 
top not only sinking below the adjacent valleys, but below the 
surface of the water as well. 
Parts of Europe and North America were especiallv well 
adapted for their formation. In Sweden they reached their 
culmination. Here they not infrequently extend for over a hun¬ 
dred miles from the interior to the sea. Their height varies from 
0 to 180 feet but probably is more often found to be between .".0 
and 100 feet. 
7. Geology, Vol. III. pp. 373-376 and 368-371, 1906. 
