Page:The Journal of geology (IA journalofgeology11893univ).pdf/278

Among five hundred bowlders examined by Mr. Buell at two railroad sections, distant less than three miles from the most remote of the parent ledges, only ten were noted that did not plainly show by rounded edges and blunted angles the effects of glacial attrition. At a point less than twelve miles distant, the abrasion had so far obliterated the surface characters that it was hardly possible to determine to which of the three classes above indicated the erratics had originally belonged. Farther on, the evidences of abrasion are still more marked. The degree of abrasion did not appear to be equally great in the case of some of the bowlders found on the crest of some of the high ridges and on the surface of the terminal moraine. Mr. Buell's observations were made with the hypothesis of englacial transportation in mind as an accepted working hypothesis, but with only meagre results in the drumlin area. Studies at two points on the slope of the outer ridge of the terminal moraine and on the edge of the overwash plain gave fifty-six bowlders that were only slightly affected by glacial abrasion and eighty-eight which showed by their rounded forms and scratched surfaces the effects of severe glacial reduction. While therefore the observations do not exclude the hypothesis of a small amount of englacial transportation, if slight abrasion be taken as sufficient evidence of this, they limit it to a quite trivial factor of the whole mass.

The combined testimony of the foregoing facts seems to me quite decisive in its bearing on the proposition that the derivation, transportation and deposit of the quartzite bowlders was almost exclusively subglacial or at least closely basal. As these bowlders enter into the structure of the drumlins from base to summit, and are mingled with much other local material, the foreign element being relatively small, they seem to compel the same conclusion respecting the whole of the material which was built into the drumlin forms.

Mr. Buell has found what he regards as satisfactory evidence that an older train of bowlders was carried directly westward at the time of the earlier drift and that the later ice movement toward the southwest crossed this train obliquely and distributed