TACOMC syst::m in rhode island. 91 



rocks. Tlio limestone l)eds are all situated iipoti the west side of tlie Blackstonc : on the 

 east side is the Cunilierland coal l)asin. 'I'lie coal rocks, however, are not confined to the 

 eastern side of the river, but cross it at Attleborougli, and extend south to Pro\ idence and 

 even to Newport upon the Narraganset bay, their western edge running nearly north and 

 south. An immense quantity of drift has been deposited over this part of the State, which 

 conceals the rock except in a few favored places. The limestone, together with its asso- 

 ciates, lies upon the western border of the coal rocks, beneath whicli they pass. With 

 these general remarks on the position and relation of the Smithfield limestone, I proceed 

 to speak of its characters, the period of its foniialion, and the rocks which aj)prar to be its 

 true associates. 



The rock in question, then, is a white or clouded liuu^stone, with a liner texture or grain 

 than the Berkshire marbles, but, like tliem, contains in mixture silex and magnesia. Some 

 portions of the rock are clouded and coarse, and with layers or strata very clearly developed ; 

 thus removing all doubts in regard to the stratification of the rock. Being, however, in 

 intimate relation to igneous rocks, it has undergone a change in texture, and acquired a 

 compactness and hardness not common to sedimentary limestones. In addition to which, 

 we find developed those peculiar minerals which have been denominated saiisxurife and 

 nephrite. These masses so intimately associated with the rocks, or developed in it, are 

 hard, compact and translucent, with a bluish tinge. They are not, however, in immediate 

 contact with the igneous masses. In a few places, again, fine greenish talc, in large spe- 

 cimens and in implanted masses, lies between the layers. The talc is in much greater 

 quantities than at any of the beds of limestone I have examined elsewhere. Without 

 dwelling, however, on those minor differences which a peculiar position seem to have 

 been instrumental in producing, I have little hesitation in saying that this rock is clearly 

 of the age of the Stockbridge limestone. It differs from the Primary limestone of St. 

 Lawrence and Essex counties, New- York, in being stratified, and in the absence of gra[)hite, 

 spinelle, or those peculiar minerals whicli are so coiuaiou in llie latter rock. 



Having satisfied myself as it regarded the age of the limestone, another question arose, 

 whether other members of the Taconic system were associated with it ; for if the opinion 

 I had formed of the limestone was correct, then some of the other members of the same 

 system ought to lie in proximity to it. 



For the determination of this question, I proceeded west from the limestone beds, and 

 observed first a slate possessing in general the characters of the magnesian slate of Berkshire, 

 Massachusetts. It occupies a very narrow belt, being restricted by great beds of granite 

 upon the west, upon which it rests. At or near the junction of the two rocks, the slate 

 and granite, I found an altered belt of slate, about one liundrcd yards wide. Again upon 

 the east of the limestone a remarkable magnesian slate appears, altered to an imperfect 

 serpentine in a few places ; in others, to an imperfect epidote, or a mineral substance whose 

 color approaches the peculiar green of epidote ; not, however, in well defined masses, but 

 in diffused green patches. Notwithstanding all the alterations the rock has undergone, it 



12* 



