TRENTON LIMESTONE. 93 



BRACniOPODA OF THE TRENTON LIMESTONE. 

 Plates XXX., XXXI., XXXII. & XXXIII. 



The BRAcniopor).\ of lliis period arc among the most numerous and prominent fossils of 

 the rock. Several species are so abundant as to constitute of themselves entire strata, and 

 others cover extensive surfaces of the thin layers. Those whicli occur in the greatest 

 profusion in New-York, arc the Orthis testudinaria ( identical witii the species of the same 

 name in Europe), and Leptcena scricca ; while other forms of Lkptjena arc scarcely less 

 abundant in some localities. In the western extension of the sanu- rock, the Delthyris lynx 

 and Atrypa protea are equally abundant ; but these species are comparatively rare in New- 

 York, and are nev'er prominent species in any localities east of Oiiio. 



The species of this order are comparatively constant and rclialile throughout extensive 

 areas, and the t3-pical species of this rock in New-York are C(|ually characteristic of strata of 

 the same age in Ohio and Indiana. It is true, tliat both in this State and in all ilic western 

 localities, many of tliese species are equall}' cliaractcristic of the upper part of this great 

 group, viz. the Hudson-river rocks. In New-York, some of the same species which mark 

 the Trenton limestone are equally abundant in the shaly sandstones of the Hudson-river 

 group ; while in the latter, we do not know of more than two species, at the present time, 

 distinct from those in the limestone below, and tiicse may yet be found in a lower position. 



It is from the occurrence of these species of Brachiopoda in tiie Hiidsou-rivcr group, 

 together with species of other genera, that I am induced to unite the whole, as before 

 stated, in one great series, though the lithological characters are so dilfcrcnt in the two 

 extremities. Among others, the Lingul.e hold a prominent place ; this limestone containing 

 half as many as we know, at present, in all the other palaiozoic rocks of America. This is 

 the more interesting, since tiiis genus, containing species of the same lype, exists in the 

 waters of our present seas, together with the Orbicula, another prominent fossil of this 

 period ; while the other genera are unknown as existing forms. 



Although the number of species of this order is nearly as great as of any other group of 

 equal thickness, still it is probable, from what we already know, that the number will be 

 increased at least one half, and perhaps doubled, when the Brachiopoda of the same period 

 in the West shall be fully known. It is probable that we shall yet discover species in New- 

 York which may swell the present number considerably, though we can scarcely anticipate 

 that we shall ever discover all those species which flourished in the more favorable conditions 

 of the western ocean of that period. 



