Chapter 3 
PRECAMBRIC HISTORY 
THE GRENVILLE FORMATION 
In the Adirondack mountains, and also probably in the Highlands- 
of-the-Hudson, we have the earliest known records of the physical 
history of New York State. These records are written in a series 
of rocks named the Grenville, so called from a town in Canada 
where the rocks were first well known. The Grenville is of in- 
terest, not only because it is the most ancient rock formation so far 
discovered in New York, but also because it takes rank among the 
very oldest rock formations of the earth. 
Until about fifteen or twenty years ago the real significance of the 
Grenville and its closely associated rocks in the Adirondacks was 
not recognized, but now many of the leading events of that very 
early history are established. As in human history, so in earth 
history, the earliest records are the most obscure and ditficult to 
read and, in the one as in the other, it is easy to pass from con- 
clusions properly based upon facts to mere speculations. Many 
problems regarding the Precambric history of our State yet remain 
to be solved, but in these pages it is rather the purpose to describe 
only those historical events: which have been well established. 
The Grenville consists of a great series of marine water-laid rocks 
_ which are clearly older than the Paleozoic because these latter rest 
upon the Grenville in many places. As will be shown below, the 
Grenville strata have been so profoundly changed from their origi- 
nal condition that certain of the highly sedimentary features have 
been obliterated. Thus the absence of water-worn particles and 
fossil shells, both of which are so characteristic of sedimentary de- 
posits, is due to complete crystallization (metamorphism) of the 
Grenville strata since their formation. Nevertheless we have cer- 
tain proofs of the sedimentary origin of the Grenville. The fact 
that these rocks commonly occur in alternating layers, which stand 
out in sharp contrast because of marked difference in composition 
and color, furnishes strong evidence that this distinct banded effect 
is due to differences in original sedimentation. A great mass of 
igneous rock is generally characterized by homogeneity throughout ; 
a mass of typical sediments, on the other hand, is arranged in dis- 
tinct layers, such as shale, sandstone, or limestone which show fre- 
quent differences in composition. In the Grenville, especially of 
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