Review of the New York Geological Reports. 



355 



With regard to the geographical divisions of this table, they 

 are to be regarded rather as grouping for local convenience than 

 as a natural classification founded upon the distribution of fossils. 



The time has, perhaps, hardly arrived for the construction of 

 a perfect chronological palasontological table, but it is probable 

 that it would recognize seven divisions, or rather three principal 

 divisions, with intervening transition series, thus : 



PROTOZOIC ROCKS, OR NEW YORK SYSTEM. 



Transition Series. 



First or Lower Division. 



Transition Series. 



Second or Middle Division. ^ 



Transition Scries. 



Third or Upper Division. 



Transition Series. 



Potsdam sandstone. 



Calciferous sandrock. 



Black River limestone. 



Trenton limestone. 



Utica slate. 



Hudson River group. 



Oneida conglomerate. 



Medina sandstone. 



Clinton group. 



Niagara group. 



Onondaga salt group/ 



Water limestone. 



Pentamerus limestone, and Catskill shaly 



limestone. 

 Oriskany sandstone. 

 Caudigalli and Schoharie grits. 

 Onondaga limestone. 

 Corniferous limestone. 

 Marcellus slate. 

 Hamilton group. 

 Genesee slate. 

 Portage group. 

 Chemung group. 



Taking into account the persistency of leading formations 

 throughout the United States, the uniformity of condition, exclu- 

 siveness and peculiar character of species in the strata embraced m 

 the three principal divisions ; and at the same time considering the 

 doubtful position which the transition series holds in the system, 

 and the apparent connecting links which they form between the 

 lower and upper rocks, this seems to us, at present, the most con- 

 sistent and satisfactory classification of these American palaeozoic 



rocks. 



We proceed \* 

 ascending order. 

 Potsdam Sandstone. — (N 



Virginia 



Reports.) This rock, the base of the New York system, and the 

 connecting link between the non-fossiliferous rocks below and the 

 fossiiiferous above, is interesting as being the oldest rock contain- 

 ing organic remains at present known in this country, and as 



