TRENTON LIMESTONE. ' 115 



the Sihirian system of Miirchison, gave it as his opinion tliat the Trenton hmestone corres- 

 ponds lo tiie Caradoc sandstone. This opinion,* founded on the supposed correspondence of 

 the organic contents of the Caradoc sandstone and Trenton hnaestone, seems, in the opinion 

 of llic writer, to have been adopted in too great haste, and from a too hmited examination of the 

 New- York rocks. It is not, perhaps, to be rejected on the ground of difference in mineral 

 cliaracter ; the Trenton being a dark shaly hmestone, and the Eiiglisli partly a pure and partly 

 an argillaceous sandstone ; still tiiis is one fact which is lo 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 Oiyptolithus 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 sji-stem. 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. actonite, 

 O. canalis, O. compressa, O. flabclhdum, O. lata, O. pccten, O. protcnsa, O. testudinaria, 

 /)«/?«., Bellerophon bilobatus, and Leptsena 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 ihe 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 Koport of 1840, Ly T. A. Conrad, p. 201 . 



