TACONIC SYSTEM IN RHODE-ISLAND. 
91 
rocks. The limestone beds are all situated upon the west side of the Blackstone : on the 
east side is the Cumberland coal basin. The coal rocks, however, are not confined to the 
eastern side of the river, but cross it at Attleborough, and extend south to Providence 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 which 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 formation, and the rocks which appear to be its 
true associates. 
The rock in question, then, is a white or clouded limestone, with a finer texture or grain 
than the Berkshire marbles, but, like them, 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 saussurite 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 graphite, 
spinelle, or those peculiar minerals which are so common in the 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 hundred 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 * 
