Review of the Neio York Geological Reports. 147 



longing to each rock are remarkably distinct. Actinolite, epidote, 

 titanium, auriferous sulphuret of iron, &c, are never found in 

 the Taconic system. 



" This brings us to the conclusion, then, that where the asso- 

 ciate minerals are different, the rocks themselves are different ; 

 and there are so few exceptions to this statement, that it appears 

 to the writer to furnish sufficient grounds for separating one sys- 

 tem from the other, by the aid of characters sufficiently important 

 and decisive for all the purposes of geology. 



"I have confined my remarks to the differences in the slates. 

 Equally important are they, when we compare the limestones of 

 the other systems with those of the Taconic. While the texture 

 and grain of the limestones of the two systems differ, there are 

 still more distinctive and specific marks which may be employed. 

 The presence of graphite in the limestones of the primary sys- 

 tem, may always be depended upon, even in hand specimens ; for 

 not an instance has occurred in which this substance has appeared 

 in the limestone of the Taconic system, or in an aqueous depos- 

 ite. 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 pe- 

 culiar constitution of graphite makes it very doubtful whether it 

 is ever produced in rocks of aqueous origin, except where they 

 have been subject 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 car- 

 bonate of lime, so far as the development of carbon from carbonic 

 acid is concerned ; and then its combination 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 charac- 

 ters, and upon associate 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, 

 such confidence is felt in the correctness 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." 



