Geology and Mineralogy. 349 



3. Channels on Drumlins : Caused by erosion of glacial 

 streams ; abstract of a paper read before the Geological Society, 

 Aug. 15, 1894, by George H. Barton. — Owing to the very 

 symmetrical form of the drumlin, with its smooth, flowing out- 

 lines, it has been able by the very equal distribution of its water- 

 shed to resist the attacks of ordinary atmospheric erosion more 

 strongly than other forms of surface. Hence to-day it presents 

 little evidence of post-glacial erosion and it is very difficult to 

 estimate the amount it has undergone during this time. 



On the other hand, of the nearly eighteen hundred drumlins 

 studied in Massachusetts under direction of Prof. N. S. Shaler for 

 the U. S. Geol. Survey, some three hundred present very interest- 

 ing features of erosion that took place after the hill had been 

 fully formed, but befoi'e the complete disappearance of the conti- 

 nental ice-sheet. 



These consist of channels varying from a few feet in width and 

 depth to those having a depth of a hundred or more feet and a 

 corresponding width. With extremely rare exceptions their beds 

 invariably slope toward the south. Very exceptionally indeed 

 the slope is towai'd the north and then only to a very slight 

 degree. 



On the ordinary typical drumlin they are found cutting along 

 either side at any elevation from base to summit, always parallel, 

 or nearly so, with its axis, or very commonly directly upon the 

 summit and coincident with the axis. A typical example of this 

 is seen on Gleason's Hill, just west of the mill, at Rockbottom, 

 Mass., where a channel, about twenty-seven feet at its greatest 

 depth, cuts directly along the axis beginning at the north end of 

 the hill at two-thirds its height and sloping southward to the 

 southern end. The hill is a symmetrical drumlin with the excep- 

 tion of this channel. 



In cases where the till is more complex in outline consisting of 

 several drumloid forms massed together, side by side, so as to 

 produce an east-west ridge as is quite common, channels of vari- 

 ous sizes occur with their beds nearly always inclined to the 

 south. Often they begin their course on the north side at one 

 half or two-thirds of the altitude, pass directly through the east- 

 west axis and down the south slope. 



In many instances eskers are found in direct linear connection 

 with the channels in such manner as to imply a relation in origin. 

 Near Worcester, Mass., there are three drumlins, each of which is 

 cut by a channel, while in the lowlands between are eskers which 

 together with the channels form a nearly continuous serpentine 

 line. Here it seems evident that the stream that formed the esker 

 must also have cut the channel. 



The streams that eroded the channels must have been super- or 

 en-glacial, to the northward of the hill, they could not have been 

 sub-glacial. Against the north end of the hill at Rockbottom the 

 ice-sheet lay massed, on or in which the stream having an ice-bed 

 had its channel. To the south the ice had disappeared or had so 



