Geology of Martha's Vineyard. 243 
and I could hardly believe the inhabitants who told me, 
that no rocks were found in place on the island. But 
wherever I had an opportunity to examine, these ledge like 
appearances vanished on a nearer approach; and the dilu- 
vial character of the surface became manifest. So that I 
feel a good degree of confidence, that the same will be 
found to be the case, with those eminences, that I did not 
visit. These loose stones vary in size, from that of the 
smallest pebbles, to that of masses, ten or even fifteen feet 
in diameter. They are almost without exception, of a 
primitive character; consisting of granite, gneiss, mica 
slate and quartz.. I saw a few masses of a pudding stone, 
similar to that of Roxbury ; but no other secondary rock, 
In short, the detritus of this formation appears obviously, 
to have been derived from the rocks, that occur in place 
along the coast, on the mainland. — 
The thickness of this diluvial mantle is not great. The 
sand from the plastic clay formation beneath it, is indeed so 
mingled with this, as to give a predominant character to the 
soil, and even the clay beneath the sand, is sometimes seen 
at the surface. In some tracts of considerable extent, little 
so indeed itis. Some fertile tracts, however, occur along 
the margin of the stnall streams, or brooks, and also in some 
instances, in the immediate vicinity of the sea: and proba- 
bly the soil in general, is of much the same character, as that 
along the adjacent shores of the continent. — , 
The character of the diluvium of the Elizabeth islands, 
appeared so precisely like that of the Vineyard, that I have 
no doubt of their indentity [say appeared, for I did not 
land on these islands; but having passed among them at 
two places remote from each other, and approached often 
within a few rods of the shore, fc k 
with their exact resemblance to t 
tour of the hills and vallies, i0 the colour, Saad 
ty of the bowlder stones, in the sandy aspect Sapte Hee 
it the high sloping sand oe so frequent along shore. 
have accordingly coloured se | | ; 
subjoined map 5 y auvial. It may be thought I do this on 
very slight grounds, but as 1 have plainly sta 
