330 RECENT CHANGES OF LEVEL 



relief by supposing that the glacial erosion has destroyed the relief which the flowing water 

 had made. From the St. Croix to the Penobscot, there is little variety in the drift marks ; 

 at Mattawamkeag the country is level, with a rather thin coating of drift, most confusedly 

 arrano-ed, there being nothing like distinct moraines at the head of the last named stream. 

 The valley is scarcely better defined than that of the St. Croix. In the table country of 

 Kentucky or Tennessee, where the rivers have about the same cutting power as here, the 

 channel section would be several times as deep. This feature of excavation increases as we 

 follow the Penobscot to the southward, and with the deepened valley comes a greater dis- 

 tinctness in the oi'dcr of the glacial debris. Near Mattawamkeag it is difficult to recognize 

 anything like distinct moraines, but when we get within thirty miles of Bangor these 

 remains become more and more distinct. Close to the latter town these terminal heaps are 

 very well marked. The fact seems to be that the retreating glacier had no local organiza- 

 tion in the upper part of the valley, while its independence was marked about Bangor. As 

 seen at a glance, the section north of Bangor presents no evidences of having been below 

 the level of the sea at the close of the glacial period. As in the localities previously dis- 

 cussed, this is to be accounted for on the supposition that the ice retained its place in suffi- 

 cient thickness to bar the access of the sea during the period of great submergence. 



In recapitulation of the evidence afforded by the detrital beds of this section of the 

 Atlantic sea board, we have the following points which are worthy of notice. 



1 . The depression of the land at the close of the first division of the glacial period, a 

 depression which seemed to increase in amount as we went from the southern to the more 

 northern regions. 



2. The return of the ice in the shape of a set of local glaciers which covered the shore 

 at Mt. Desert, and along most of the territory, at least as far as New Brunswick, persisting 

 until the final re-elevation of the land to near its present level. 



From the inspection of the coast of Maine alone it is not possible for us to form any sat- 

 isfactory judgment as to the time which has elapsed since the passage of this secondary ice 

 sheet. The evidence obtained on other parts of the coast of the North Atlantic, and 

 among the mountains of Europe, points to the conclusion, which is very general in its way, 

 that a period of at least ten thousand years must have elapsed since this great change 

 took place. This point will be seen to have an important bearing on the matter of the 

 re-elevation of the shore, when this comes to be considered in the final section of this 

 report. 



THE EXCxVVATION OF THE ICE TIME. 



In reports on the glacial history of Narragansett and Massachusetts Bays,^ I have con- 

 sidered somewhat in detail the action of an ice sheet working over a surface of irregular 

 hardness. I shall not repeat here the matter discussed in those papers, but only recapitu- 

 late briefly the general conclusions which are necessary for our present inquiry. The 

 following propositions I regard as established. 



1. That the fiord zone results from the irregular wearuig of the rock surface traversed 

 by the glacial sheet ; the whole of the surflxce within the glacial tract wherever the difier- 



1 The report on Massachusetts Bav is not yet pubh^^he^l. 



