Observations on Trilobites. 3 87 



is described as such in the former part of this paper ; a single 

 individual differing sufficiently from this to entitle it to be 

 considered as a separate species, was afterwards brought to 

 New- York by Mr. Sherman, by whom this interesting locality 

 was first explored. Of Chambered Univalves, one species of 

 Nautilus occurs, and three of Orthocera. One of the latter 

 is peculiar in its figure, and will probably, on examination, 

 prove a species that has not been fully described ; this pecu- 

 liarity consists in its being composed of two conical frus- 

 trums of very unequal dimensions, contracting suddenly at the 

 place of junction. A specimen of this kind in the collection 

 of Mr. Sherman of Trenton, is nearly 3 feet in length ; by the 

 continual action of the water it has been worn down to 

 the axis, and exhibits, in a striking manner, the position and 

 formation of the Septa? and Siphunculus ; from its shape it is 

 vulgarly supposed to be the petrifaction of a large animal of 

 the Lizard species ; a similar mistake is said to have been 

 made by Whitehurst, in relation to an Orthocera from Derby- 

 shire, probably an analogous specimen. 



No univalves without chambers have hitherto been found. 



Of bivalves, the specimens exhibit several species of Tere- 

 hratula and Producti. 



Nature of the formation. Organic remains furnish the most 

 decisive evidence of the identity or difference of formations. 

 Judging from those which occur at Trenton, we should 

 consider the rock to belong to the transition class, the 

 submedial of Coneybeare and Philips. This deduction is 

 founded on the presence of the Calymene Blumenbachii, which 

 the united testimony of Buckland, Coneybeare and Philips, 

 and Brongniart ascribe to that order of rock. Were it not for 

 this, the small inclination of the strata might have been con- 

 sidered as entitling it to be arranged as a part of the first 

 floetz formation of Werner, or it might have appeared from 

 the number of Entrochi or Encrinitic vertebrae, to belong to 

 fhe mountain limestone of English authors. Eaton is there- 



