MORRILL-BBLPAST BAY SYSTEM. 145 



tern is shown by the deep cut at the road to consist of till. A central ridge 

 of till was covered on both slopes by 10 or more feet of glacial sand and 

 gravel, some of it reaching the top of the ridge, and snbsequentl}^ the whole 

 was buried beneath several feet of marine clay. This suggests the ques- 

 tion whether a core of till may not often occupy the central and basal por- 

 tions of the low rounded ridges of the discontinuous systems of glacial 

 gravel. I have examined a large number of the lenticular masses char- 

 acteristic of this type of gravels, and this is the only case where they could 

 be proved to contain unmodified till. Yet these excavations seldom went 

 to the bottom of the deposit, and their number is small as compared with 

 the whole number of similar bodies. It is possible a till nucleus may be 

 somewhat common in these mammillary kames. 

 The length of the system is about 1 1 miles. 



GENERAL NOTE ON THE BELFAST REGION. 



It will be seen that five gravel systems converge to Belfast Bay. The 

 glacial scratches last made converge to the same place, while the earlier 

 scratches were more nearly parallel. The discontinuous systems of gravel 

 are, therefore, nearly parallel with the scratches last made, and they appear 

 to date from the last part of the Griacial period. Most, perhaps all, of the 

 discontinuous systems expand at some point into delta-plains, the largest of 

 which are situated at or not far below the contour of 230 feet. Toward the 

 south the gravel deposits become .smaller and the intervals between them 

 longer. 



The large island of Isleboro lies in the midst of Penobscot Bay, to 

 the south and east of Belfast, and in the line of these systems prolonged. 

 The island shows a limited amount of beach gravel, but no glacial gravel 

 that I could find. Three of the Belfast Bay gravel systems come down to 

 the shore, but their diminishing size toward the sea indicates that there was 

 probably no large development of glacial gravel over what is now the sea. 



LOCAL ESKEKS IN TROY AND PLYMOUTH. 



A broad, level region covered by marine clay extends from Unity 

 Pond northeastward through Troy. It is continuous with a line of sedi- 

 mentary clay extending northward through Plymouth and Detroit to the 



MON XXXIV 10 



