114 GLACIAL GRAVELS OF MAINE. 



direction, and in so doing taking its way in all directions from southwest 

 around to south, southeast, and even east, by this time one will- see how 

 irresistible is the proof that such a river must have been confined between 

 ice walls to flow so independently of the surface forms of the land. Yet 

 it did not flow wholly independently of them. It nowhere crosses hills 

 more than 200 feet liigher than the ground to the north of them, and thus 

 it penetrates the high ranges only along low passes. Traveling southward, 

 for two days before reaching the Morrison Pond Pass I had observed that 

 remarkable gap through them, and at a venture assigned it as the gateway 

 of the osar river. For a day and a half after the idea came to me the osar 

 continued a nearly south course, and it often seemed impossible it could 

 go so far to the east. But at last in the Sunk-haze wilderness it described 

 a long and regular curve to the left and shot straight for its natural outlet 

 between the hills. 



This osar affords interesting points as to the retreat of the ice north- 

 ward before the advancing sea. To say nothing of the delta-plains depos- 

 ited in reentering bays or broad channels within the ice up which the sea 

 extended, we have at least two and perhaps three series of delta-plains 

 deposited in the open sea. First, the ice over the Narragiiagus Valley 

 melted, so that the delta-plains west and northwest of Deblois were formed. 

 Subsequently the ice disappeared over the valley of Union River, which 

 then became covered by the sea. This arrested the further flow of the 

 glacial river southeastward. For a time it continued to flow into the bay 

 of the Union River Valley, and the Silsby Plains in Aurora were thus 

 deposited. Still later, the ice receded up the valley of the Penobscot until 

 the osar river probably poured into the broad Penobscot Bay of that period 

 in Greenfield. The broad, plain-like ridges near the Penobscot River at 

 South Lincoln, though deposited between ice walls, may have been hi part 

 due to the checking of the glacial water at that point by the advance of the 

 sea. The same thing may have happened at the mouth of the Pattagum- 

 pus, and the apparent plains of valley drift near the junction of the Seboois 

 and the East Branch of the Penobscot may be eitlier fluviatile or estuarine 

 drift, brought down from above by glacial streams while the country to the 

 north was still covered by ice. The pinnacles of Greenbush and several 

 other enlargements of the gravel deposits were probably deposited in glacial 



