532 THE JOURNAL OF GEOLOGY. 



They differ from the osar type in their marginal relation to the 

 ice and their transverse arrangement. There is, however, a gra- 

 dation between the two, and no sharp line of demarkation has 

 yet been found ; probably none exists. But there appears to be 

 this important genetic difference : the typical kames appear to 

 be the products of relatively active vigorous glaciers, while the 

 typical osars appear to be the products of extremely inactive, if 

 not stagnant, glaciers. This important difference of significance 

 is thought to amply justify the recognition of the two classes 

 whatever may be the difficulties in sharply separating them. 



The difficulties of sharply discriminating between the osar 

 type and the kame type are increased by the fact that there is 

 a class of gravel ridges having forms precisely like the typical 

 osars, that lie more or less transverse to the glacial movement. 

 These yet await thoroughgoing investigation, but I incline to 

 the belief that they are to be regarded as true osars, and that 

 they were formed during the stagnant conditions of the ice just 

 before its disappearance, their transverse course being due to the 

 control of the underlying topography. It has been stated that 

 the course of the osars was conditioned partly upon the direction 

 of the ice movement and partly upon the topography of the land 

 surface. In this instance, it appears that the land topography 

 dominated the osar formation, and that the movement of the ice 

 became uninfluential. In support of this view it may be added 

 that some osars on reaching the border of the ice turn to a course 

 nearly parallel with it. 1 



(2). Osar [esker) deltas or fans. — It appears that when the 

 glacial streams reached the border of the ice sheet and were free 

 from bounding ice walls, they spread themselves out widely and 

 dropped a large portion of their burden in the form of deltas or 

 fans. These are not uncommon in the interior as well as in 

 Maine, where the osar phenomenon has its most remarkable 

 development in America. These deltas are very significant both 



1 Dr. Lundbohm has directed my attention recently to the fact that this is a not 

 uncommon phenomenon in Sweden, as shown by the geological maps of the Swedish 

 Survey. 



