146 Review of the New York Geological Reports. 



an isolated group, distinct from the primary, and yet not meta- 

 morphic palaeozoic strata : he has given them the name of Ta- 

 conic system, since they exist on both sides of a range of hills, 

 known by the name of the Taconic mountains, running north 

 and south, almost coincident with the eastern boundary line of 

 the State. He admits that the slates and shales composing this 

 system closely resemble the lowest fossiliferous schists ; but en- 

 deavors to prove that they can not be these latter strata altered, 

 because there is a want of similarity in the position of the rocks 

 of the Taconic system and those fossil-bearing strata to which 

 they are referred ; " for," says he, " we do not expect that by any 

 agent, a slate can be changed into a limestone, nor is it likely to 

 be ; neither will the order of superposition be changed by meta- 

 morphism." Admitting this, we do not consider the argument 

 altogether conclusive, because, according to Dr. E., the Taconic 

 series is of great thickness, and though, in its present upturned 

 and contorted position, it occupies but a narrow belt, when spread 

 out of course had a much greater superficial area: but equivalent 

 beds, identified by their fossils at distant localities, may be sand- 

 stones or argillaceous deposites in one place, and a limestone in 

 another. The Taconic rocks may have title, as Dr. E. contends, 

 to be considered a distinct system, but fully to establish this, de- 

 mands, we think, other and more decisive evidence. 



Dr. E.'s arguments in proof that the strata under consideration 

 are distinct from analogous primary beds, is founded on difference 

 in texture, color, association, chemical composition and mineral 

 contents. Comparing them, he remarks : 



" Taking, for example, the talcous slates of the two systems, I 

 have no hesitation in saying that constant and reliable differences 

 exist, and may be found in all careful and close examinations. 

 These differences exist in the quality of the slates themselves, 

 particularly in the color and lustre of the laminae, and their pe- 

 culiar contortions. But more decided differences are found in the 

 associations of the rocks. The talcous slate of the primary sys- 

 tem is universally associated with hornblende or soapstone, or 

 both ; while the talcous slate of the Taconic system is never as- 

 sociated or connected with either of these rocks ; or, to state the 

 fact in other words, never passes into them, whereas, in the for- 

 mer case, it does. Another fact of the same nature is also well 

 determined by observation, viz. that the imbedded minerals be- 



