Summary. 



It will be seen that these grooves, with the accompanying strise, lie two 

 miles or more south of the drift margin,* as located by Lewis and Wright. 

 All grooves of large size heretofore observed lie many miles back from the 

 front of the drift, unless with the single exception (so far as known to the 

 writers) of the groove on Table rock, at the Delaware water-gap, observed 

 by Lewis and Wright, f which lies ten miles behind the moraine. 



It may be said that these grooves do not lie south of the drift margin, for 

 Lewis has described " the fringe," consisting of isolated or grouped erratics, 

 as extending some miles in front of the moraine in this neighborhood. The 

 fact remains, however, that the grooves are south of the terminal moraine, 

 as mapped and described by Lewis and Wright. Whether the discovery of 

 these phenomena indicates that the line of the moraine must be drawn fur- 

 ther south in this locality, or that these grooves do really lie outside the 

 terminal moraine, cannot at present be positively stated. It has been sug- 

 gested that "the fringe" is the mark of the first glacial epoch, and that 

 possibly the grooves may belong to that epoch. 



In the states of Ohio, Indiana, Illinois, Iowa and Nebraska, Chamberlin 

 records strise outside the terminal moraine and inside the drift margin, but, 

 so far as the authors are aware, no large grooves have been reported as 

 occurring in that interval. 



Glacialists are pretty well agreed that the eroding power of the ice-sheet 

 decreased toward the margin, where it was thinner and lighter. That 

 grooves of the size of those here seen could be carved in the massive and re- 

 sisting sandstone at the very margin of the ice-sheet seems well-nigh in- 

 credible. They lie at an angle of 45° to the direction of the old valley, of 

 which the base-level plain forms the floor, and (looking in their reversed 

 directiou) are directed towards the western-bounding hill of the plain, which 

 is here exceptionally abrupt and 250 feet in height, having cliffs of the 

 harder strata along its front. That any conceivable ice-sheet could have 

 descended such an abrupt slope and, after having advanced one-fourth to 

 one-half a mile from its bottom, could make the observed grooves, is almost 

 beyond belief. But the gouges and strise within and accompanying the 

 grooves make thus much certain, viz., that if the large channels so well seen 

 on Kelly's island in Lake Erie and elsewhere are glacial grooves, the 

 grooves described in this paper must also be so classed ; for their similarity, 

 amounting almost to identity of appearance, precludes any difference in 

 origin. 



*The nearest strise reported are half a mile northwest of Newcastle; Loc. cit., p. 196. 

 fLoe. cit., pp. 85, 87. 



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