xtI introduction. 



included in the Wcniock fornialiou of England, Passing upward, on the other hand, to 

 the red sandstone, containing remains of peculiar fishes so analogous to those of the 

 British Isles, lliat we unhesitatingly refer the rock to the Old Red Sandstone of Europe ; 

 we find the formation separated by an unequivocal line of demarkation from the rocks 

 Ix'low, which arc charged with shells and trilobites. So abrupt and well defined is this line, 

 that in undisturbed regions we have no difiiculty in recognizing it by the sudden and entire 

 ceasation of brachiopods alone, while usually the lithological cliange is more distinctly 

 marked by a coarse sandstone or conglomerate. Whatever may be said, therefore, of the 

 identity in age, and the mingling in the same formation, of Devonian fossils, such as 

 Brachiopoda, Acephala and Gasteropoda, with the peculiar fishes of the Old Red Sandstone 

 in Great Britain, such a condition never happens in the United Slates, so far as observations 

 have extended.* 



At the present time, I am obliged to recognize the following great subdivisions as in- 

 dicated by zoological characters. Commencing with the lowest rock known to contain 

 fossils, we find the first important change in the typical forms to occur at the termination 

 of the Hudson-river group ; which is marked by a coarse sandstone or conglomerate 

 (the Oneida conglomerate or Shawangunk grit), beyond which scarcely a single species 

 has prolonged its existence. This point must be considered as representing that horizon, 

 which, in Great Britain, is the termination of the Lower Silurian deposits. We never find, 

 however, in the succeeding groups, a mingling of the fossils of the lower and higher rocks, 

 which is regarded as taking place in England and Wales, where the strata are much 

 disturbed. 



The Pentamerus oblongus, so well known and extensive in its geographical range, is 

 never found in the United States associoted with the fossils of the lower division. On the 

 other hand, it occurs in a calcareous band among shales and sandstones, far more naturally 

 belonging to the succeeding higher strata than to the lower. Moreover, although found in 



* Id the State of New- York, and in other parts of the United States, the most natural and obvious arrangement 

 woald be to include in one system all the strata to the termination of the Chemung group ; since, as already shown, 

 there is no lithological change more obvious or important at the base of these higher furmations, than tiiere is at the 

 ban of the Niagara and Clinton groups. Where the Oriskany sandstone is absent, it is even scarcely possible to 

 diatiligliisb the line of separation between the Niagara and Cornifcrous limestones, though one is regarded as of 

 Deronian and the other of Silurian age. If we consider any one class of fossils as a guide in determining the limits of 

 ■jralMia, thro perhaps the peculiar " Devonian fishes," which first appear in our Schoharie grit, or at(the base of 

 tbe Onondaga limestone, will be regarded as indication of the commencement of a new era. Still, however, the 

 character* of the other classes of fossils is not materially changed, and several species of the central part of the system 

 have prolonged their existence into the superior strata. The zoological question, therefore, is to be tested upon the 

 ground, whether the commencement of a certain order of fishes at a certain period is more important than the 

 •abaeqnent change, when all the other classes of organic remains are exterminated, and the same order of fishes is 

 coatiDoed? 



