DRUM LIN, OSAR AND J^AME FORMATION. 26 1 



hypothesis that the erratics rose in the ice and were transported 

 englacially in any considerable degree. In this case, the great- 

 est accumulation should have been at the terminal moraine where 

 the ice halted longest. It seems to be also difficult to under- 

 stand, on the hypothesis offered by Mr. Upham, how the drum- 

 lins lying immediately on the ledges and immediately in their lee 

 could have been filled so largely with quartzite- bowlders. Cer- 

 tainly the bowlders could not have risen in the ice so high as to 

 have become exposed at its surface by ablation and then have 

 been overflowed by a new accession of ice and moulded into the 

 drumlin form, and at length have been let down by the melting of 

 the ice beneath without more forward movement than observation 

 shows. The simplicity of the facts do not seem to tally with 

 the complexity of this theory. 



3. The amount of abrasion which the bowlders suffered bears 

 specifically upon the question of the mode of their transporta- 

 tion. The parent outcrops gave rise to erratics of three kinds, 

 (i) In Paleozoic times the ledges stood as islands in the seas, 

 and there accumulated about them very coarse conglomerates of 

 quartzite. From these, a portion of the erratics were derived in an 

 already rounded condition. The character of this rounding and 

 the superficial changes the pebbles underwent before the glacial 

 period made it possible for Mr. Buell to distinguish these with 

 measureable certainty in following the train until abrasion had 

 destroyed their surface characters. (2) Talus blocks accumu- 

 lated about the bases of outcrops before the ice invasion that 

 formed the drumlins. There was an earlier invasion which bore 

 quartzite erratics westward. The later invasion bore them south- 

 westward. The talus blocks under consideration are, perhaps, in 

 the main, those that were derived from the quartzite knobs in the 

 interval between the two. They are distinguishable from blocks 

 disrupted by the ice by means of the weathered character of 

 their several surfaces, so long as these remain unabraded. (3) 

 The third class of erratics are those that were derived by direct 

 action of the ice upon the parent knobs. These are distin- 

 guished by their unweathered fracture surfaces. 



