GLACIAL DEPOSITS. 69 



formed at the front of the ice. The same evidence is visible at the present 

 time, though less distinctly, in similar cuttings which are making from 

 Brockton southward. The result of these irregular movements of the ice 

 has been to give the drift deposits of this field a peculiarly irregular and 

 confused character. The greater part of the eskers or ridges of sand, gravel, 

 and bowlders which were formed within the ice-carved channels that were 

 excavated by the subglacial streams has been effaced. 



It is a notable fact that in the southern part of the basin, on the shores 

 and islands of that part of it which is included in Rhode Island, eskers are 

 essentially absent, except near the moraine which borders the western 

 margin of the field. This seems to be due, not to the successive advances 

 and recessions of the ice front, but rather to the fact that the very deep chan- 

 nels of the bay provided ample low levels through which the subglacial 

 streams made their way to the sea. In the district between the railway 

 bridge at Somerset and Steep Brook Station there is an extensive and very 

 characteristic area of those ' ' pitted plains " which are often found near where 

 a subglacial stream discharged its current into open water. The area 

 which now remains is evidently only a fragment of the original field. The 

 materials seem to have been brought to their position by an under-ice 

 river which followed in general the line of the present Taunton River. The 

 cause of the pittings is not yet determined, but they are probably due to 

 the embedding of masses of ice in the swiftly accumulating detritus, these 

 small bergs being weighted down to the bottom by the amount of rocky 

 matter which they contained; when they melted, the originally level 

 surface fell into its present shape. 



The till or bowlder-clay coating of this district is, on the average, less 

 thick than in the region lying immediately to the northward; wherever the 

 section extends to the bed rock this most general element of the drift — the 

 waste dropped on the rocks in the last retreat of the ice — is commonly found 

 to have a thickness of less than 10 feet. Although this till sheet, when it 

 covers rounded masses of the bed rocks, often takes on a drumlin aspect, it 

 seems clear that there are none of these peculiar lenticular hills in the basin. 

 Their absence on the margin of this part of the continental glacier is in 

 accord with their distribution in other parts of this country; they are 

 evidently due to the conditions which prevailed in the portion of the ice 

 which lay near the margin, but not usually within 50 miles or so of its verge. 



