MOOSEHEAD LAKE OSAR. 127 



finer sediment which was more nearly horizontally stratified than the coarse 

 gravel of the ridge formed in the narrow channel. 



There is much silt and clay covering the upper part of the valley of 

 Black Brook I have no accurate data as to the difi"erence of level between 

 the Notch and the Piscataquis River. By measurements with the aneroid, 

 taken at several hours' interval, the difference is but little short of 100 feet. 

 If so, the clay of the valley of Black Brook near the Notch is not due to 

 the floods of the Piscataquis, being higher than the terraces of that river. 

 Besides, these clays are so abundant that it seems improbable that so large 

 an amount of sediment could be carried several miles along a backwater 

 lake. A much more probable theorj^ is that the clays were deposited late 

 in the Ice period, when the broad channel of the osar-plain had become 

 still further broadened and the ice next the hills had melted, so that the 

 A'alley of Black Brook formed a lake between the hills on the southeast and 

 the ice which still covered the valleys of Black Brook and the Piscataquis 

 River to the northwest. This lake would for a time overflow southward 

 through the Notch, and would cease to be a lake when the ice over the 

 Piscataquis Valley had melted so that the waters could escape along the 

 present lines of drainage. Into this lake considerable mud would for a 

 time be brought by glacial streams. 



Just at the north end of the Notch the gravel system is joined by a 

 tributary branch. It appeared to be short. I traced it for one-fourth of a 

 mile, when it seemed to end. I afterwards regretted that I did not explore 

 the country to the north, as it is possible a discontinuous series of kames 

 may extend in that direction. The osar-plain is fully one-eighth of a mile 

 broad at the north end of the Notch, and extends southward about one-half 

 mile. Then for another half mile, where the steep hillsides almost meet at 

 the bottom so as to form a V-shaped valley, a few very round cobbles and 

 bowlderets are found here and there and testify that the osar river flowed 

 through the Notch. The force of current must have been very great in 

 order to leave so little gravel in the valley. Bare ledges abound, yet here 

 and there considerable areas of till have escaped denudation. The till was 

 the fine clayey till characteristic of the slate regions. The rounded osar 

 stones distinctly overlie the till, and therefore must have been deposited at 

 a later stage. I made no excavations, and do not know with certainty that 

 there are no rounded osar stones mixed with the till, but in the banks of a 



