106 GLACIAL GRAVELS OF MAINE. 



the Sandy, shows that the sedimentary deposits are very nearly the same 

 in all of them. These valleys are all at about the same distance from the 

 .sea and the sediments may well be interpreted by comparison. In some 

 of these valleys, as the Pleasant and Carrabassett, the sediments are plainly 

 overwash or frontal plains, composed of matter that was brought down by 

 glacial streams to the extremity of the ice and then spread out over the 

 bottoms of the open valleys. They mark a stage in the retreat of the ice 

 when it still lingered in the upper parts of these valleys and practically 

 formed local valley glaciers. Since a true osar river flowed from the north 

 into the gorge of the Seboois River and also in the lower part of the valley 

 of the East Branch, the history of these valleys is probably this: A long 

 osar river at one time flowed through the valleys. Later the osar expanded 

 -to an osar-plain in the gorge of the Seboois and for some miles down the 

 East Branch. Finally, on the retreat of the ice the lower portion of these 

 valleys was covered by a frontal plain of sediments derived from the glacial 

 rstreams of the glacier that still lingered near the head waters of the Seboois 

 Valley. 



At Medway this osar crosses the West Branch of the Penobscot, and, 

 except an island in the river, has been washed away by it. The osar then 

 follows the south bank of the river for about 3 miles, being washed away in 

 some places. Just west of the mouth of Pattagumpus Stream there is, on the 

 south side of the river, a plain of high reticulated ridges, forming a jumble of 

 hummocks and hollows. The gravel here is coarser than the average of the 

 ridge. The osar for 3 miles has been taking a nearly east course, and directly 

 before it lay the broad Penobscot Valley. The osar river, leaving this 

 •valley of natural drainage, turned to the right through a deflection angle 

 of nearly 135° and took a southwest course up the Pattagumpus Valley, 

 then over a low divide and down a branch of Maddunkeiink Stream into 

 'Chester. Near the Penobscot River it turns southwestward and follows the 

 west side of that river for several miles, and then at the north end of 

 Hocamoc Island it crosses to the east side (PI. IV, A). The north end of 

 this island is composed in part of the osar gravel. South of this point the 

 gravel takes the form of a series of massive ridges or plains, separated by 

 short gaps. These ridges are 20 to 50 feet high, and are rather level on the 

 .top, in places gently rolling and containing shallow hollows. The system 



