Geology of Martha’s Vineyard. 241 
Vineyard ; and forma part of the south east barrier of Buz- 
zards Bay. They contain a few scattered inhabitants. 
In my route from the city of Boston, I passed over the 
well known puddingstone of Roxbury and Dorchester; the 
argillite and greenstone of Quincy; the sienite and sienitic 
granite of Braintreeand Weymouth, with its beautiful dykes 
of basalt, or greenstone; the gray wacke slate? of Abington; 
the diluvium of East and South Bridgewater; the gray 
wacke slate, diluvium and singular talcous rock, containing 
feldspar, of Middleboro ; and struck at New Bedford, upon 
mica slate, hornblende slate, and gneiss, inter-stratified, and 
eontaining beds and veins of granite, In sailing out of New 
Bedford harbour, these latter rocks appeared occasionally, 
for several miles.along the shore; and., I was led to antici- 
pate their continuance as far.as Elizabeth Islands and Mar- 
tha’s Vineyard: but on. passing the former, I perceived a 
diluyial coat to be spread over theirsomewhat hilly surface; 
while the shores, in many places, exhibited steep, declivities 
of sand. And on reaching the north western shore of Mar- 
a’s vineyard, I found its aspect to be very similar These 
islands so far as 1 have examined them, appear to be. made 
up of the three following formations :, 1 Alluvial ;.2 Diluvi- 
al: 3 Plastic Clay. these terms in the Modern re- 
stricted sense ; that is, as the latest writers employ them, io 
describing the strata of England and France. I take’for a 
‘standard, the late work of Conybeare and Phillips, on the 
geology of England and Wales. + 
1 Alluvial. ne ee é 
This formation, occupies a considerable _portic 
southern part of the Vineyard ; reaching in, some places, 
even beyond the centre of the island 
isiand, — z 
it consists of a perfectly level, sandy tract, uninhabited and 
uninhabitable. I have rarely seen as extensive a region, 
that was so cheerless and barren. 
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