WALDOBORO MORAINE. 273 



2. Duriug the gradual shrinking of a glacier no frontal naorainal ridge 

 can be formed. The morainal matter is left scattered promiscuously over 

 the field of retreat. 



3. When the rate of flow of the ice equals or nearly equals the rate of 

 melting at the ice front, a rather steep rid'ge must form at the end of the 

 glacier. 



It thus appears reasonably certain that the Waldoboro moraine was 

 not formed during an advance or recession of the extremity of the ice, but 

 during a time when the rate of advance or flow of the ice at that point very 

 nearly equaled its rate of melting. South of Winslows I have found no 

 similar ridge. It is a fair inference that during the time preA'ious to the 

 period of this frontal moraine the ice had been melting faster than it was 

 replenished by flowing ice from the north. Here for a time the two rates 

 were nearly equal, allowing-, however, for two or three little periods when 

 the ice receded a few rods and then held its own again. Then the rate of 

 melting gained on the rate of ice flow, and as the front retreated northward 

 the country was covered with a diffused sheet of till. 



To the north of this moraine lies a gently rolling plain for a few miles, 

 and then we come to a range of round-topped hills rising 500 to 800 feet 

 above the sea. This plain would be rather favorable to the flow of ice south- 

 ward up to a very late date. The moraine crosses several hills. Its highest 

 point is about 150 feet above tide water. At this point it crosses the north- 

 ern spur of a hill which toward the south rises near a hundred feet higher than 

 the moraine. If the ice had much exceeded 150 feet in thickness, it ought 

 to have reached a hig-her point on the hill than it did.^ If we assume a 

 thickness of less than 200 feet of ice at the time of the formation of the 

 moraine, we must admit that it is jJi'obable the higher hills of Washing- 

 ton and Liberty, situated north of this place, rose above the surface of 

 the ice at that time. If moraines then formed on the ice from matter slid- 

 ing down from the hills, we ought now to find lateral moraines bordering 

 the valleys that lie between these hills, and thence extending south to the 



' Observations in Greenland and by Eussell in Alaska prove that when a rock or hill rises in the 

 midst of a glacier the ice is driven far up the stoss side of the obstruction, sometimes to a height of 

 several hundred feet. If this sort of action took place at the hill crossed by the moraine east of 

 Winslows Mills, the thickness of the ice may have been even less than the above estimate. The ice 

 did not reach so far south ou the hillside by an eighth of a mile or more as it did in the valleys situ- 

 ated east and west of the hill. This, perhaps, may prove that the ice over the hill dragged behind 

 the deeper ice of the valleys because it there bulged somewhat above the general level of the surface. 

 MON XXXIV 18 



