A GRANITE-GNEISS IN CENTRAL CONNECTICUT 
THE granite-gneiss* to be described occurs on both sides of 
the Connecticut River, some five miles east of Middletown. It 
cuts the schists of the eastern crystalline area of Connecticut, a 
short distance east of their contact with the Triassic sandstone. 
Its distribution is shown on the accompanying map (Fig.1).? It 
forms an oval area inthe mica schist, and, at its northern end, 
is continued northward by a series of beds varying from a few 
inches to many feet in thickness, lying parallel to the enclosing 
schists. The largest of these is a direct continuation of the 
main granite-gneiss mass, and all are probably parts of the same 
intrusion. As the distance from the main area increases, these 
beds gradually thin out and disappear from the schists. 
The only previous work on the geology of this region is that 
of Percival,3 who recognized this granitic rock only on the east 
side of the river, and united that part of it with a large mass of 
granitic-gneiss to the north, with which it is probably not con- 
nected. He does not consider the origin of any of the gneisses. 
It ‘has not been possibie to use Percival’s results except in a 
general way, and the work done in this region by the writer is 
essentially de novo. 
The rock is a medium to fine-grained biotite-gneiss. The 
color varies from white or light gray to dark gray, according to 
the amount of biotite. In a few cases the rock is almost or 
quite massive, but usually it is well foliated. The granite-gneiss 
is cut by several sets of joint planes, of which one set is nearly 
"In this paper a gneiss of granitic composition and of unknown origin is called 
a granitic gneiss; if of igneous origin, a granitic gneiss. See C. H. GorDON in Bull. 
Geol. Soc. America, Vol. VII, p. 122. 
2 That portion of the western boundary of the granite-gneiss north of the river is 
largely covered by river terrace, and for about a mile along the eastern border, near 
Great Hill pond, outcrops are rare. With these two possible exceptions, the “sup- 
posed boundary,” so-called, is believed to be very nearly the true boundary. 
3J.G. PeRcIVAL: Report on the Geology of Connecticut. 1842, pp. 222, 224. 
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