TESTS OF SLTBGLACIAL OR SUPERFICIAL DEPOSITION. 431 



to the slopes of the land. It is doubtful if contiuuity or noncontinuity 

 furnishes a crucial test between the two kinds of streams, but the pheno- 

 mena near the coast make it probable that noncontinuity is a distinguishing 

 feature of an early stage of subglacial sedimentation. 



SIZE OP THE OSARS. 



If, as I assume, the only supei"ficial streams (if there were any) that 

 were concerned directly in osar formation were situated near the ice 

 front, then the probability of such a stream forming a large ridge is not 

 so great as that a long subglacial stream would form one. The only 

 way such a stream could make a very large ridge is retreatally, and 

 even then it is difficult to account for one, especially for the stratified osars. 

 For sedimentation in the present stratified condition could not have 

 begun till the ice in the bottom of the superficial channel was melted, 

 and since that would happen only late, it seems improbable that a very 

 large ridge could collect after that time before the ice was all melted. 

 The great size of such ridges as the Whalesback, Aurora, favors the 

 subglacial hypothesis. 



LOCAL VERSUS PAR-TRAVELED MATERIAL. 



Professor Chamberlin has shown that in the West the osars are com- 

 posed of local matter clearly differentiated from the euglacial till, which 

 was derived from the distant crystalline hills. His argument is that sub- 

 glacial streams would reach the local matter, whereas superficial streams 

 would rarely do this, but their sediments would consist of englacial matter 

 from a distance. 



Several disputed questions are involved in the application of this argu- 

 ment to Maine, such as the manner in Avhich basal ddbris got up into the 

 ice, the angle of its supposed ascent, the height it attained, etc. In many 

 places in Maine I have not been able to draw so fine distinctions as those 

 of Professor Chamberlin between subglacial till of local and englacial till of 

 distant origin. There are multitudes of places, especially in eastern Maine, 

 where local matter appears in the upper part of the till within a few feet or 

 rods from the northern edge of an outcrop of rock. This is especially 

 noticeable in the case of granite bowlders. Whether this is subglacial or 

 englacial till is a question for determination. I have not always been able 



