UPPER AND LOWER TILL. 83 



rock is slate. The till next the rock is intensely tough and claj'^ey, being 

 mostly derived from the clay slate. The ridge proper rests on this sheet 

 and contains a large proportion of granitic matter derived from the granite 

 outcrop near Mount Katahdin. The ridge has a sort of lamination, as if 

 accumulated in successive layers parallel with its arched surface; yet it is 

 true till and at the exposures examined contains no sedimentary matter. 

 Near East Vassalboro and elsewhere are a few symmetrical cones which on 

 the surface are composed of sandy till. They are found suspiciously near 

 the discontinuous kame systems, and this suggests genetic relationship with 

 the conical and lenticular kames. As suggested elsewhere, a glacial stream 

 that plunges down a crevasse will enlarge its shaft at the bottom and form 

 a conical cavity, in which a conical kame will collect if the stream brings 

 down coarse sediment. If the stream should for some reason cease to flow 

 at this place, it is possible that till might subsequently collect in the ice 

 cavity around the original kame as a nucleus ; and if little or no gravel col- 

 lected in tlie cave, still it might in some way become filled with till after the 

 flow of the stream ceased. 



Irregular heaps and ridges of till, which appear to be mostly composed 

 of englacial matter, abound in all parts of the State. When these are 

 mapped and masses of the ground moraine distinguished from the englacial 

 till, it will be possible to write out almost the whole history of the ice 

 movements. The till is more unequally distributed in the granitic and 

 coarsely schistose regions than in the areas of slates and sedimentary 

 rocks, and its distribution is more irregular near the coast than in the 

 interior. 



THE UPPER AND LOWER TILL. 



The upper layers of the till are less compact than the lower, perhaps 

 owing in part to the heaving of the frost. No doubt frost has in some 

 cases brought up bowlders toward the surface, and this partly accounts for 

 the fact that most of the larger bowlders are found on or near the surface, 

 but only partly, for in the granitic regions bowlders are often piled one 

 above another in such a manner that the frost can not have changed their 

 relative positions, and here the larger bowlders are more often at the top. 



The most probable interpretation of the facts is that the finer and more 

 intensely glaciated lower portion of the till was deposited in its present 



MON XXXIV 3 



