INTRODUCTrON. XVU 



a lower calcareous band, it cannot be separated by any important lilhological or zoological 

 characters from a succeeding one, in which we find fragments of Bumastis barriensis, and 

 other fossils typical of the middle division of our system. Indeed, so well marked is the 

 position of this fossil, that throughout a large part of New- York, and at intervals in a 

 western direction, extending even beyond the Mississippi river, it holds its unequivocal 

 place in the series ; never mingling with the abundant lower forms, nor rising far above 

 the base of the second great division of the system.* 



At the same period, and associated in the same rock with the Pentamerus, commences 

 the Catenipora escharoides, which, though sometimes regarded as of little importance in the 

 identification of strata, has nevertheless a very limited geological range. This coral extends 

 from the Clinton group to the top of the Niagara limestone, in which rock it becomes 

 abundant and widely disseminated, marking unequivocally that horizon over more than a 

 thousand miles in extent. 



After leaving the first division of the system, we are able to recognize in the subordinate 

 groups many zoological affinities, from the Clinton group, to the commencement of the 

 Oriskany sandstone ; beyond which, very few of the preceding forms continued their 

 existence. Although the details of all these groups are not yet wrought out, we are quite 

 confident that the result will prove the correctness of our position.! 



With the Schoharie grit, commences a series of strata containing fossils as distinct 

 from those of the preceding formations, as these are from the lower division. We here, 

 for the first time, recognize several species that are regarded as Devonian forms ; and if 

 zoological characters are to be paramount, we are compelled to unite all the succeeding 

 strata as of Devonian age. There is, however, no greater distinction to be observed at this 

 horizon of change, than at the previous one ; and if the two lower divisions are considered 

 parts of one system, then the succeeding one should constitute the third term in the same. 



I shall hereafter be able to show more clearly the zoological relations of these successive 

 subdivisions, after having given as thorough a revision of the whole series, as I have been 

 enabled to do of the groups of the lower division. 



* After examining a collection of fossils from the Lower Silurian strata of Great Britain, collected from authentic 

 localities, I am inclined to believe that the Pentamenit oblongus holds the same position there as in New-York ; 

 occurring above the conglomerate or breccia, which, there as in this country, forms the true limit of Lower Silurian 

 ■trata. The disturbed condition of the rocks in that country has probably so interplicated the strata, as to produce a 

 mingling of the fossils of two periods ; which has given rise to the conclusion that this fossil, with a few others of the 

 same period, are Lower Silurian ; while from a mingling of Wenlock forms with these, there is afforded no line of 

 demarkation so clear and unmistakable as we have in the United States. 



t The Delthyris shaly limestone bears many affinities, both in lithological and fossil characters, with the Niagara 

 group. Several of the brachiopods have been considered as identical, but a careful comparison proves them quite 

 distinct in the two groups. 



[PALiEONTOLOOY.] O 



