Ei. Hitchcock on a Bowlder in Amherst, Massachusetts. 399 
and grooving should be deeper, and the edges less rounded, (as 
they are) than by what I suppose to have been the subsequent 
ye the bowlder was a part of the ledge from which it was bro- 
en. In that case it must have been turned over after starting 
being able to move it, were forced over it, ; 
Ifa strong cael were thus crowding detritus against and 
over the bowlder, its oblong form would keep its longer axis in 
the same direction as the stream. Hence the smaller fragments 
forced against and over it, would smooth the top and the sides 
in the same direction. They would press most heavily upon the 
top, and accordingly the strize are much deeper there than upon 
the sides, though it should also be recollected that the edge of 
stratum is usually harder than its face. 
_ I impute the parallel striation of this bowlder, then, first to 
its great weight, which caused smaller fragments to slide over it 
more or less; and secondly, to its oblong form, which kept it 
nearly in the same position while advancing. 
The only strive on this bowlder not yet described, are a few 
faint ones running obliquely across the present north end, (the 
