166 
GEOLOGY OF THE FIRST DISTRICT. 
the boulders and pebbles form a beach, and for a time protect the clilf; but these are gra¬ 
dually ground up by the action of the surf, or swept away. These cliffs are from twenty to 
one hundred and forty feet high. 
The boulders and pebbles of these cliffs consist principally of granite of a rather fine grain, 
with a base of red feldspar and smoky quartz. The mica is small in quantity, and in many 
blocks is absent. Coarse granite, gneiss, hornblende rock, greenstone, some mica slate, tal- 
cose slate, chlorite slate, hornblende slate, and red sandstone, were observed. 
The red granite is similar in aspect to that extending from Stonington north-northeast 
through Voluntown (Con.) and Foster in Rhode-Island, and is properly a thick-bedded gneiss ; 
but in ordinary sized boulders, would be considered and described as granite. The coarse 
granite can be referred to granite veins of similar characters in Rhode-Island; the gneiss also 
to Rhode-Island. The hornblende rocks (some of the masses at least) are peculiar, and I 
have seen such in place only in the east part of New-London and Windham counties in Con¬ 
necticut, and the west part of Rhode-Island. When wet, it is quite green, almost like the 
carbonate of copper. The hornblende slate is like the range of that rock, extending from 
Groton in Connecticut, through Preston, Plainfield, Brooklyn and Thompson into Massachu¬ 
setts, and contains chlorite and epidote as common minerals.* It is peculiar in its aspect, 
and the layers much contorted. The greenstone is compact trap, like the dykes that traverse 
the gneiss rocks in Windham, Lebanon, Marlborough, &c. in Connecticut, and those of the 
region around Smithfield and southwest of Newport in Rhode-Island. The mica slate was 
like the range of mica slate extending from Bozrah in Connecticut, through Hampton, Pom- 
fret and Woodstock, into Massachusetts. The talcose and chloritic slates were like the meta- 
morphic slates, that may be classed under those names, on the island of Rhode-Island. A 
single pebble of a rock that has been found in place in Naragansett bay, only, was found. It 
is an altered metamorphic rock, that has been called greywacke, and talcose slate, but is pe¬ 
culiar in its aspect, and contains fiat, black, tabular crystals. The red sandstone, when first 
seen, was supposed to have been left there accidentally, transported by human agency ; but 
afterwards I saw it in numerous places on the hills, on the beaches, and in the cliffs over most 
of this part of the island, called Shawango neck. It is perfectly like the red sandstone of 
Chatham in Connecticut, where it is extensively quarried. Nearly all the rocks mentioned, 
even the large masses imbedded in the cliffs, had their edges and angles more or less rounded 
off, and very many of the smaller masses were rounded pebbles.t The minerals observed in 
*■ This range of rock is described as “ contorted gneiss and hornblende slate,” in my Sketch of the Geology and Mineralogy 
of New-London and Windham counties in Connecticut. (Norwich, 1834, p. 12.) 
t On the neck between Great pond and Fort Pond bay, which was once an island, great numbers of boulders were 
seen. They were generally similar to those of Shawango neck. A reef of rocks (boulders and blocks, it is believed,) 
extends out some distance from the shore, on the northern extremity of this neck at Culloden’s point, an indication of the 
wasting away of the land. The same fact may be observed on Shawango neck at Jones reef, about a mile west of Mon- 
tauk point, and at Shagwam reef, about three miles west of the same place. This latter reef extends out north about 
three miles from the shore, and is supposed to be composed of blocks and boulders that have remained after the washing 
