44 GLACIAL GKAVELS OP MAINE. 



the waves strike the shore obhquely. As the result of all these causes,, 

 together with the tidal currents, the projecting parts of the land are denuded 

 of loose matter, while the bays and coves are strewn with beach gravels. 



Such are some of the most common modes of wave action as exhibited 

 along the present beach. Rising above the beach cliffs, we find that a con- 

 siderable part of the island of Mouhegan is bare of soil. The local rocks 

 weather very unequally. Many of the bare ledges of coarse-grained 

 syenitic granite have already been shattered into bowlders and cliff debris. 

 "Wherever the rock weathers slowly the rounded forms of the roches 

 moutonndes are beautifully exhibited. Everywhere a thin layer on the 

 surface has weathered away, and I could find no glacial scratches on rock 

 long laid bare. On the north shore was a place where the surf had recently 

 undermined and removed the till. Here the scratches were well preserved 

 and the rock bore every appearance of having been as violently glaciated 

 as it was anywhere on the mainland. It thus appears that the rounded 

 bosses of rock which cover a large part of the island are true roches 

 moutonndes and owe their shapes to glacial action. As the ice-sheet passed 

 over the island, it ought to have left as large a proportion of the surface 

 covered with till as it did elsewhere on that coast. But the proportion of 

 bare rock is unusually great on this island. If we assume that the whole 

 surface was originally covered with till, we find that the greatest amount of 

 work that can be assigned to wave action at levels above the present beach 

 cliffs consists of (1) the erosion of a considerable part of the till, and (2) 

 some attrition, which may have erased the glacial scratches but did not 

 obliterate the characteristic forms of the roches moutonn^es. When we 

 compare the ragged and uneven cliff of erosion at the present beach with 

 the still moutonne'ed ledges at higher levels, it becomes evident that the sea 

 has stood at or near its present position many times as long as at any liigher 

 level. At the higher elevations the surf had time to erode the till from the 

 more exposed shores, but it had not time to form a cliff of erosion in the 

 solid rock before a change of level transferred the wave action to higher or 

 lower rock. In other words, the changes of level of the sea were relatively 

 rapid. 



In a few places undisturbed till was observed resting on the glaciated 

 rock, but over most of those parts of the island covered by soil the super- 

 ficial deposits consisted of a formation needing careful study in order to 



