140 
GEOLOGY OF THE SECOND DISTRICT. 
Stance has occurred in which this substance has appeared in the limestone of the Taconic 
system, or in an aqueous deposit. Besides, the instances are not very numerous in which 
any minerals of the primary rocks are found in this system. White pyroxene and tremolite 
do occur at a few localities ; but the peculiar constitution of graphite makes it very doubtful 
whether it is even produced in rocks of aqueous origin, except where they have been subjected 
to the powerful action of melted lavas, or to the influence of caloric in some other mode. 
Molecular action, unaided by heat, is insufficient to effect the decomposition of carbonate of 
lime, so far as the development of carbon from carbonic acid is concerned; and then its com¬ 
bination with metallic iron, to complete the chemical constitution of this substance, appears to 
be still more difficult, Wlrerever graphite exists, we may rest satisfied with the conclusion 
that the agency of caloric has been there, and in a state too of great intensity. 
If then reliance can be placed upon lithological characters, and upon associated minerals, we 
may raise something more than doubt as it regards the identity of the Taconic rocks with the 
true Primary system, or certain members of it. In truth, much confidence is felt in the cor¬ 
rectness of the principles which have influenced me in proposing their separation, and that 
they possess characters fully sufficient to give them an independent place in the systems of 
the day. 
Error has often arisen, in not making the distinctions here insisted upon; or it has been 
more easily fallen into, by the frequent proximity of the two kinds of limestone to each other, 
and their near approach to identity, where mere texture and crystallization is concerned. 
Thus, along the Hoosic mountain range, we often find the true Primary limestone very near 
the Stockbridge limestone ; and both being often dolomitic, and of a coarse texture, and more 
than this, composed of carbonate of lime, it is a sufficient reason why the two should be 
regarded not only as one mineral, but one rock. But I trust that in the preceding part of 
this report, I have already said enough to place this subject in its true light: the reader is 
accordingly referred to pp. 37-67. 
After what has been said of the slate and limestones of this system, I deem it unnecessary 
to speak of the general characters of the granular quartz rock, which occurs in mountain 
masses in the same system. It is sufficient to observe, that in position, it does not correspond 
to any of the sandstones or siliceous rocks of the New-York system, and cannot therefore be 
regarded as a metamorphic rock; for example, an altered mass of the Potsdam sandstone. 
If the preceding views are admissible, there is sufficient reason for regarding the rocks 
which lie between the upper members of the Champlain group and the Hoosic mountain, as 
a distinct series at least; but I would remark, that by the expression, “ lying between,” I 
have reference to geograpical position ; for considered geologically, they can be regarded in 
no other light than as inferior to the Potsdam sandstone, or as having been deposited at an 
era earlier than the lowest member of the New-York Transition system. We have in no 
instance, however, been able to trace a connection in these masses, and we have never found 
the Potsdam sandstone resting upon any of the members of the Taconic system. To attempt 
to explain this remarkable feature, or fact, would be premature. The bare fact that the 
Potsdam sandstone rests on gneiss or granite, without the interposition of any other rock, we 
early pointed out; and commencing our series with it, we find it to be unbroken and unin- 
