GRANITE-GENISS IN CONNECTICUT 653 
occurs (2) as a white, fine-grained granulitic portion of some of 
the pegmatites. (3) One or several dikes of gray granulite cut 
the dark gneisses which occur associated with the granite-gneiss 
along its northern border (Map, 5). Their position is shown on 
the map. Each of these varieties has its own peculiarities and 
all differ from the contact granulite. They are probably all 
later than this last and are merely mentioned here for the sake 
of completeness. 
5. Darker and more foliated granite-gneiss—Along the north- 
eastern side of the granite-gneiss area is a belt which has already 
been noticed, in which the granite-gneiss alternates with schists 
and with dark, more or less hornblendic gneisses and amphib- 
olites. This area is indicated on the map. Associated here 
with the granite-gneiss and with these other rocks is a third 
type, in a way intermediate, yet more closely related to the 
granite-gneiss. These last rocks are darker and more foliated 
than the granite-gneiss. They are frequently marked by lentic- 
ular-linear white patches, up to a third of an inch in thickness, 
composed of an aggregate of feldspar grains. From this char- 
acter they may be named “‘spotted-gneiss.”” They agree micro- 
scopically in structure and in mineral composition with the 
granite-gneiss. There are only two differences: (1) anincrease 
in the amount of biotite and, asa consequence, a better developed 
foliation, and (2) the presence in some cases of hornblende. 
Sometimes they show microscopical evidence of crushing. They 
form eruptive contacts with the schists which are cut by the 
granite-gneiss. 
The relations of the spotted-gneiss and the amphibolites are 
not wholly clear, and these relations are probably different in 
different cases. The two rocks are distinct petrographically. 
The contact between the two is an eruptive contact. If the 
amphibolites are older——-and their stronger banding and folia- 
tion might well suggest as much—it matters not to the under- 
standing of the granite-gneiss whether they are of igneous or 
sedimentary origin; they are in either case earlier rocks cut by 
the granite-gneiss. But in many cases they are probably later. 
