30 NEW YORK STATE MUSEUM 
the northwestern and southeastern Adirondacks, there are extensive 
beds of crystalline limestone, such as the Gouverneur marble of St 
Lawrence county. Such rocks could not have been of igneous 
origin. In many places, and sometimes in sharp contact with the 
limestone, are beds of almost pure quartz rock, which are certainly 
not igneous but which represent original sandstone layers. Again, 
there are very extensive deposits throughout the Adirondacks of 
generally darker colored rocks rich in such minerals as quartz, feld- 
spar, garnet, mica, pyroxene, and amphibole. These rocks, because 
of their constant close association with the strata just described as 
well as their banded structure, are also clearly ancient sediments. 
The composition of these latter rocks shows that the original sedi- 
ments were muds, often with sand or lime. Another argument in 
support of the sedimentary character of the Grenville is the presence 
of flakes of graphite (plumbago) which are so commonly dis- 
seminated throughout the formation. In some places the strata are 
so filled with graphite that the mineral is mined, as in Essex and 
Saratoga counties. Carbon existing under such conditions is prob- 
ably of organic origin and represents the final stage in the decom- 
position of organisms which lived in the waters while the Grenville 
strata were lbeing deposited. The occurrence of so much garnet is 
also at least highly suggestive because this mineral is especially 
common in crystallized sediments in many parts of the world. 
Having established the sedimentary origin of the oldest known 
formation in New York State, we are led to the interesting and 
important conclusion that this Grenville formation is not the oldest 
which ever existed in the State. The Grenville sediments must have 
been deposited, layer upon layer, upon a surface of still older rocks. 
A knowledge of the character and composition of such Pregrenville 
rocks would be of very great interest, but thus far we have no 
positive evidence that such rocks are visible in the Adirondacks, 
although certain rocks still of somewhat doubtful age and origin 
may belong to that very ancient rock floor. Again, the fact that 
Grenville sediments were being deposited under water carries with 
it the corollary that there must have been land somewhere at no 
great distance from the area of deposition because then, as now, 
such sediments as muds and sands could have been derived only 
from the erosion or wearing away of land and have been deposited 
in great sheets one above the other, under water adjacent to the 
land mass. Here, too, we are as yet utterly in the dark so far as 
any knowledge of the location or character of that very ancient land 
is concerned, 
