60 GLACIAL GRAVELS OF MAINE. 



northern ends of some of the osars and in some of the smaller hillside 

 kames the stones are biit little waterworn, and the same is true of the stones 

 at the margins of some of the osar-plains and of the smaller solid kame 

 plains. On the other hand, the large stones of the coarse valley drift from 

 the swift mountain streams are often quite well waterworn, though seldom 

 as much so as those of the kames and osars. With the exception of these 

 steep vallej'-s among the hills, whenever in Maine we find a plain of appar- 

 ent valley di-ift composed of stones considerably rolled and rounded, we are 

 sure to find one of the following conditions : 



1. A short distance up the valley the stream may have eroded a 

 ravine or channel tlu-ough a deep mass of till. In this case the stones are 

 those of the eroded till, which were worn and rolled at the rapids formed 

 while the stream was cutting through the till barrier. Such a formation 

 occurs at Kingman and at many other places. The proof in such cases is 

 not complete unless it appears that the deposit of well-rolled stones extends 

 only a short distance below the channel of erosion, and that beyond that 

 point the character of the valley drift changes. 



2. If we trace both northward and south^vard such a plain of much 

 worn stones, we may find it leaving the valley and going up and over liills 

 to other drainage basins, or it may leave the Ijottom of the valley and go 

 up along a hillside as a sort of terrace. In these cases the apparent plain 

 of valley drift is an osar-plain, or broad osar, happening to occupj' the 

 bottom of a valley. 



3. To the north such a plain of highly rounded stones ras.j end in a 

 kame or osar, while to the south the plain becomes finer in composition, 

 passing from gravel to sand, and finally to clay. In this case our plain of 

 well-rolled stones is a frontal plain of glacial sediments, consisting of matter 

 that AA^as brought down by glacial streams to the extremity of the ice (i. e., 

 the end of the osar), and there was poured out into the open valley. From 

 that point southward the sediment is spread across the bottom of the valley 

 like purely flu-\datile drift, yet the stones received their shapes almost 

 entirely while being transported in the ice channels of the glacier, which at 

 the time of deposition lay to the north. Several such frontal or overwash 

 plains are described elsewhere. 



In addition to the above-named glacial or semiglacial deposits, we also 

 find, in a few valleys having a northward slope, sediments that were dropped 



