208 REPORT ON CORRELATION 
wide distribution throughout the area, and form dikes, stocks, and 
small laccoliths. 
All these intrusives preceded a great period of metamorphism. 
Following it and still antedating the Potsdam, there entered two 
series of narrow dikes: one of basaltic rocks, which are very widely 
distributed, and a minor set of syenite-porphyry. 
The oldest Paleozoic sediment anywhere in the Adirondacks is 
the Potsdam sandstone. 
From the above it is evident that in this area the pre-Cambrian 
formations are practically the same as those in the neighboring parts 
of Ontario and Quebec. 
IV. RESUME OF THE GEOLOGY OF THE EASTERN ONTARIO AREA 
The area presents an immense development of highly metamor- 
phosed rocks, for the most part of sedimentary origin. Among these 
limestones preponderate. ‘These limestones in the southern portion 
of the area, where the metamorphism is less intense, are often fine 
in grain and drab or bluish in color. On going north, however, 
there is a progressive increase in the intensity of metamorphism, 
and the limestones gradually lose their color and become coarser in 
grain, eventually developing into coarsely crystalline white marbles, 
generally more or less impure. 
Interstratified with these limestones are non-calcareous rocks, 
among which fine-grained, often more or less rusty weathering 
gneisses and a variety of amphibolites are the most important and 
the most abundant. A few bands of quartzite also occur, although 
in this area these are distinctly subordinate 
These gneisses certainly represent highly altered and recrystal- 
lized sediments, more or less argillaceous in character. The quart- 
zites are in the majority of instances altered arenaceous sediments. 
Adams has shown that the amphibolites have a threefold origin. 
Certain of them represent limestones which have been altered by 
invading granites; others have been produced by the dynamic 
alteration of basic igneous intrusions; while still others have in all 
probability resulted from the recrystallization of basic fragmental 
volcanic material. The remarkable fact is that all these processes 
produce amphibolites which cannot be distinguished from one another 
