Feb., 1907.] The Columbus Esker. 65 



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 (') 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, haA^e 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 ox 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 inaximum 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 closely 

 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. Not infrequently they extend 

 from a stream valley up and across a low divide of 200 feet 

 (sometimes 400 feet) and down again into a A'alley 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 reachecl their 

 culmination. Here they not infrequently extend for over a hun- 

 dred miles from the interior to the sea. Their height varies from 

 to 180 feet but probably is more often found to be between ilO 

 and 100 feet. 



7. Geology, Vol. III. pp. 37.3-376 and 368-371, 1906. 



