GLACIAL DRIFT. 255 
Mr. Joseph Dow, of Hampton, says a measurement of the bluff in 1875 
showed that a length of one rod at the point had disappeared since 1826; 
and his impression is that a prominent stone, called Gunning Roék, near 
the end of the boulders, is farther removed from the bluff now than it 
was forty years since. 
A view of this bluff from either side near the end shows finely the 
distinction insisted upon in this report between the lower and upper till. 
The sides of the bluff meet 
Upper till. 
at the end, making a sharp on 
edge, which dips towards the 
east at an angle of 60°. Fig. ome 
wer fill. 
54 is copied from a photo- 2 
graph, which shows the line Fig. 54.—SECTION OF Boar’s HEAD. 
between these divisions as plainly as in nature. The upper part has 
been broken away near its end, but its depth is nearly uniform over 
the whole plain, about ten feet, or a little less, at the end. This has its 
usual reddish-yellow in distinction from the bluish cast of the lower till. 
It is ferruginous, comparatively loose in texture, and contains rough 
stones, rarely any that have been striated, and the material is chiefly 
the slates found in place two or three miles distant. Being easily 
crushed, the upper till contains an unusual proportion of earth. Its 
resemblance to the upper till of Portland, Me. is obvious. The lower 
thirty-five feet of till is composed of very compact, gritty earth, slightly 
clayey, containing numerous smoothed and striated boulders, from grains 
of sand to fifteen feet in length. Many of the stones are in the condi- 
tion of unstable equilibrium. The uncovering of the boulders by wash- 
ing enables us to learn their nature, and refer them to their probable 
source. A careful description of the different kinds observed here 
will illustrate the origin and dispersion of all the boulders along the 
sea-shore. The most abundant rock is sienite, boulders 12 and 15 feet 
in length occurring occasionally. Those 6 feet long are common. They 
are all glaciated, but many have been smoothed since falling out of the 
bank by the waves. It is gray with a considerable sprinkling of white. 
I will group the boulders according to size. Of those about six feet in 
length are sienite, gneiss, trap, Pawtuckaway sienite, granite with blue 
feldspar, such as occurs in ledges at Frost’s Point in Rye, crumpled 
