146 NEW YORK STATE MUSEUM 
of the Grenville by carbonic acid. Can the same be said for the 
other minerals such as calcite, chalcopyrite, etc. or were they 
admitted through the walls of the cellular structures by fissures 
after the manner of geodes as described by van Tuyl (8) as solu- 
tions depositing their mineral content in the above order? In 
the lack of evidence for this latter method for the formation of 
these minerals it seems very likely that they were due in part 
to recrystallization from solution of the original Grenville as well 
as to crystallization from solutions introduced with the silica- 
bearing waters when the walls and brecciated fragments were 
being replaced. As a breccia is the most favorable place for the 
circulation of mineral-bearing waters, it would not be unreason- 
able to suppose that this was the method of vein filling. 
Effect of Vein Filling upon the Wall Rocks 
Underlying the coarse reddish pink marble or d of footwall sec- 
tion is a bed c of silicified Grenville. The hand specimen shows 
the constituents to be quartz, pink and colorless calcite, phlogo- 
pite, irregular and circular areas of light and dark green kaolin 
and occasional sphenoidal crystals and irregular grains of chal- 
copyrite. Under the microscope, the calcite and phlogopite prove 
to be much older than the quartz and to have been replaced by the 
latter. The irregular or circular areas of dark and light green 
substances appear to consist of alteration products of phlogopite 
such as kaolin, tale (?), vermiculite and limonite. As scapolite 
is quite a common constituent of the marble it is quite possible 
that some of these may be due to its alteration. 
This rock has in all probability been transformed into its 
present condition from one very much like the Grenville marble 
through the permeation of silica-bearing solutions. This silifi- 
cation decreases in its effect toward the over and underlying 
strata of the footwall section, as shown by the increasing dom1- 
nance of calcite over quartz in the vicinity of both. 
The presence of drusy quartz veins and replacement phenomena 
in the pyroxene gneisses and hornblende pegmatites of the hang- 
ing wall series would indicate not only a later origin for the 
quartz but also that it doubtless was a part of the same event 
which effected not only the footwall member but also an after 
effect or concomitant event with the main silification of the 
vein breccia. 
