Feather stonhaugh's Geological Report. 81 



their impressions, showing that the same species lived and died 

 in the same localities. A great variety of forms belong to this 

 family, and new genera are constantly being discovered, per- 

 haps some of them, as the agnostus pisiformis, may be the 

 young of another kind, before the change of form. Some of 

 the species are faund identically diffused in very distant parts 

 of the earth. 



The bivalves of this group consist of a very preponderating 

 number of the brachiopode family, the producta, spirifera, and 

 terebratula. The fossiliferous beds of this group are generally, 

 in all parts of the world, characterized by these shells, and 

 sometimes almost entirely consist of them. The spirifera re- 

 ceive their name from one kind having a spiral structure inside, 

 which is calcareous in calcareous fossils, and siliceous where, 

 as frequently happens in the calcareous beds of the United 

 States, the fossils are entirely siliceous. The producta appear 

 to have become extinct before the deposition of the oolitic 

 system, and the spirifera only to have been continued into the 

 first beds of that series. The terebratula have survived them 

 both, and exist now as recent shells. The cardia^ likewise 

 having a strong resemblance to existing shells, are contem- 

 poraneous with the last. 



All these families of marine fossil remains are found in this 

 lower group in the United States. In the lower limestones of 

 the Shenandoah valley, in Rockingham county, both trilobites 

 and ammonites are found. Near Kingsport, in Tennessee, 

 orthocera abound in the same formation, as well as other spiral 

 concamerated shells. At Trenton falls, in the State of New 

 York, fine specimens of trilobites are collected. A great num- 

 ber of localities might be added. 



Mr. Agassiz, in his work,* gives admirable figures of the 

 fossil fish' found in this group. In this remarkable production, 

 the author has begun to throw light from another source upon 



* Recherches sur les Poissons FossUes. Neuchutel, 1835. 

 6 



