334 GLACIAL GRAVELS OF MAINE. 



Instances are elsewhere recorded (see p. 161) where streams and 

 springs have eroded portions of the glacial marine deltas and exposed till 

 strewn with bowlders just like the ordinary till of the locality, or where 

 the delta is thin the tops of the larger bowlders project above the gravel. 



3. Bowlders having rounded and polished surfaces are found within or 

 partly within the glacial gravels. These must be as truly a part of the 

 formation as the finer sediments. There are multitudes of them in the 

 gravels of south westerm Maine of all sizes up to 6 feet in diameter. 



4. Elsewhere are described certain large bowlders found in the northern 

 part of Baldwin. They are situated on a northern slope in the midst of 

 medium sand, and have little or no water polish. The sand is horizontally 

 terraced in such a way as to suggest that the bowlders were deposited by 

 floating ice in a broad osar channel which contained a lake-like body of water 

 confined between the ice on the north, east, and west and the hill situated to 

 the south. An alternative hypothesis is that the broad osar channels were 

 overarched by ice resting upon the w^ater that collected north of the hills. 



5. In the case of the larger ice channels, especially the superficial 

 ones, floating ice would often transport stones and bowlders like any other 

 river ice. I do not know how in all cases to distinguish whether a bowlder 

 not polished and rounded was di'opped from the ice into the bed of the 

 glacial river, or was transported b}^ floating ice, or was driven along by ice 

 gorges. We know that ice dams to-day are efficient means of transporting 

 large bowlders. Not many years ago in Rowland an ice gorge of the 

 Piscataquis River forced upward a very large bowlder 10 feet out of the 

 bed of the river and left it on the silty flood plain several rods back from 

 the channel of the river. The ice gorges of the osar channels must have 

 been efficient means of transporting bowlders and leaving them in the 

 midst of fine sediment. 



6. Bowlders not water-polished are found here and there on the surface 

 of the osar border clay, i. e., the clay deposited in a very much broadened 

 osar channel. These broad channels were from one-eighth to near three- 

 fourths of a mile wide, and it is extremely improbable that they were 

 subglacial. The few stones and bowlders they here and there contain were 

 almost certainly di-opped by floating ice. If arched by ice for so great a 

 width, it was probably sustained by flotation on the underlying water. 



7. There are considerable numbers of bowlders not waterworn, which 



