Geological Reports on the State of Neio York. 13 



we not expect to find all the organic remains of such periods to consist 

 chiefly of one group of species over the whole globe, especially when we 

 find the flora of the carboniferous era to have been every where nearly 

 the same? Are not rocks of the oolitic group in South America, the 

 cretaceous, and even the eocene of North America, mere extensions of 

 European systems, deposited in seas of the same periods, and containing 

 the same groups of shells ? Deeper oceans and greater variation of tem- 

 perature have cast more uncertainty over the upper tertiary formations, 

 but the transition affords us the converse of this proposition ; greater uni- 

 formity of temperature, a more perfect identity of organic remains, and 

 rock masses of more uniform character. That the sea of one of these 

 ancient eras was shallow, is proved not only by its universality, but by the 

 ripple marks and fucoides which every where pervade the strata. A 

 negative evidence is also supplied in the nature of the fossils. Dr. Buck- 

 land has shown how admirably the complicated chambers, and the exte- 

 rior surface of the Ammonites were constructed, to resist the pressure of 

 deep water. But shells of this genus were not created until more pro- 

 found seas had resulted from changes in the configuration of the earth's 

 surface, subsequent to the deposition of the coal formations. The Go- 

 niatite, which has a plain exterior, and septa simply angulated, is un- 

 known in that part of the transition we have termed the Trenton group ; 

 and in the upper part of the series it is among the rarest of the univalves, 

 abounding only in the carboniferous epoch. The cephalapods, which 

 flourished in the lower transition, were reduced to the simpler structure 

 of the genera Cyrtoceras, Gyrthoceras, and a few kindred forms, with plain 

 arched septa, like the nautilus. There is also reason to believe that the 

 brachiopods of the transition, so different from the prevailing form of the 

 superior strata which constitute the genus Terebratula, were, unlike the 

 latter, denizens of very shoal water. Immense numbers lived and were 

 entombed with the remains of terrestrial plants on the margins of islands 

 in the carboniferous epoch. The bituminous shale of the coal measures 

 is in some places stored with a species of Producta with long filiform 

 spines, all the specimens having the two valves in their natural position, 

 and the spines broken off from the shells simply by pressure of the su- 

 perincumbent strata. They were never subjected to the action of a 

 stormy surf, and yet land plants grew in the vicinity of the living shells ; 

 hence we infer a quiescent state of the waters around the islands of the 

 transition eras. But one exception has been noticed, which occurs at 

 Rochester, in a thin layer of limestone full of broken Pentamera; in 

 other places, single valves of bivalves occur, but the entire shells are so 

 remarkably abundant, that whatever may have been the force of currents 

 originating the breccias and conglomerates, the waters were remarkably 

 quiescent during the deposition of shales and limestones." 



