TRENTON LIMESTONE. 
115 
the Silurian system of Murchison, gave it as his opinion that the Trenton limestone corres¬ 
ponds to the Caradoc sandstone. This opinion,* founded on the supposed correspondence of 
the organic contents of the Caradoc sandstone and Trenton limestone, seems, in the opinion 
of the wi'iter, to have been adopted in too great haste, and from a too limited examination of the 
New-York rocks. It is not, perhaps, to be rejected on the ground of dilference in mineral 
character ; the Trenton being a dark shaly limestone, and the English partly a pure and partly 
an argillaceous sandstone ; still this is one fact "which is to be taken into consideration, and so 
far as it goes, is against this opinion. But leaving out of view the diversity in lithological 
characters, I see still stronger objections in the organic contents of the two rocks. The 
Cryptolithus tessellatus of Green, for example, is given as a Caradoc fossil, and is considered 
as a synonyme of the Trinucleus carractaci of Murchison, or to be the same fossil; this is 
unquestionably an error. The Cryptolithus of Green is confined to the Trenton mass, but it 
is by no means the Trinucleus carractaci of Murchison : the latter I have found in the Lor- 
rain shales, and have been able to identify it with the carractaci given in the work on the 
Silurian system. I would remark here, that it would be better to adopt the generic term 
Trinucleus, in the place of Green’s name, Cryptolithus. It will then stand Trinucleus tes¬ 
sellatus ; which, so far as observation has extended, is confined to the Trenton limestone. 
If the Trenton limestone is not equivalent to the Caradoc sandstone, to what rock in the 
English- series is it equivalent ? To this question, though it is not possible to give an answer 
perfectly satisfactory, yet I consider it quite safe to remark, that it appears probable that it is 
the Bala limestone of the Cambrian system. If fossils are to be received as evidence, they 
go far to confirm this view ; thus, among its fossils are the Orthis anomala, Schlot., 0. actonias, 
O. canalis, 0. compressa, 0. flabellulum, O. lata, O. pecten, O. protensa, O. testudinaria, 
Dalm., Bellerophon bilobatus, and Leptaena sericea. (See Murchison’s Silurian System, p. 
308.) But the geological position of the Trenton is still more conclusive ; for on this side of 
the Atlantic, it is beneath the rocks equivalent to the Llandeilo flags. There is interposed, 
therefore, several hundred feet of rock between the Trenton limestone and Caradoc sand¬ 
stone ; which, taken in connection with the facts just stated, seems to set aside the opinion of 
those geologists who have regarded this limestone as the equivalent in this country of the 
Caradoc of the Silurian system. 
I am induced to believe that the disturbances in the English rocks, especially in the lower 
part of the Silurian system, are such that their composition is extremely obscure, and that 
many of the masses are not so well developed as in this country, and hence we find great 
difficulty in recognizing them. I am sensible that it is not so much our business to be seek¬ 
ing for geological equivalents, as to describe clearly our rocks, and to determine distinctly 
their relations and their order of superposition ; still, the work of identification is not useless, 
and we may derive much satisfaction in discovering the coincidences of position and of cha-^ 
racter between rocks so remote from each other. 
See Report of 1840, by T. A. Conrad, p. 201. 
