392 GLACIAL GRAVELS OF MAINE. 



from Clifton to Penobscot Bay is about the same as from Otis to the mouth 

 of the Union River. If the sea that rose on the land was so warm that the 

 ice melted before it as fast or almost as fast as the sea rose, then the ice 

 would have retreated in the Penobscot Valley to Clifton as soon or nearly 

 as soon as it retreated to Otis in the other valley. This would arrest the 

 flow eastwai'd of the glacial river. If any delta formed in Otis it would 

 have been very small instead of large, as it really is. The same reasoning 

 applies to the overflow to Aurora. 



Several inferences follow. Although the sea was deeper in the Penob- 

 scot Valley, yet the retreat of the ice was relatively slower in this valley 

 than in that of Union River. Part of this difference may be due to the 

 southeastward motion of the ice, but in any case we know that the ice 

 could flow into regions below sea level and maintain itself for a considerable 

 time. The sea was cold, and ice in it melted slowly. Comparing two val- 

 leys, both beneath the sea level of that time, the one most favorably situ- 

 ated for a rapid flow of the ice showed a slower rate of retreat than the 

 other, where the flow of the ice from the north was embarrassed by trans- 

 verse hills. 



Elsewhere are described the glacial lakes that were formed near Lead 

 Mountain, Beddington. These were formed in level grounds south of hills 

 that would early arrest the flow of ice from the north. For man}^ miles the 

 glacial river that deposited gravels in these lakes flowed a half mile or more 

 west of the Narraguagus River and on ground 50 to 100 or more feet above 

 it. During all the time the glacial river was flowing into the lakes the 

 deeper river A-alley was filled with solid ice to a point south of tliQ lakes at 

 least. In other words, the ice in lee of hills melted sooner than the ice 

 in the adjacent north-and-south valley favorable to a rapid flow from the 

 north. This happened above the highest sea level. 



Thus both above and beneath the sea we have proof of a lobate fi'ont 

 during the retreat of the ice, but thus far no definite means of comparing 

 the relative rates of retreat in the two cases. 



The lines of synchronal retreat were drawn on the map (PI. XXXI) 

 to connect deposits independentl}^ determined to belong to approximately 

 the same stages of retreat, as set forth in detail in the table. When the 

 given points are so few it is manifestly impossible to exhibit the narrower 

 sinuses and lobes that probably marked the actual lines of retreat. 



