INTRODUCTION. 
XVII 
a lower calcareous band, it cannot be separated by any important lithological 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 Pentamerus oblungus 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 
strata. 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. 
f 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. 
| Paleontology.] 
c 
