140 GEOLOGY OF THE SECOND DISTRICT. 



Stance has occurred in whicli this substance has appeared in the hmestone 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 tremoHte 

 do occur at a few locahtics ; but the pecuhar 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 Irom 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. Wherever 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 hmestone 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 v/ould remark, that by the expression, " lying between," I 

 have reference to geograpical position ; for considered geologically, tliey can be regarded in 

 no other light than as inferior to the Potsdam sandstone, or as having been deposited at an 

 era earlier tlian 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- 



