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 palaeontological table, but it is probable 

 that it would recognize seven divisions, or rather three principal 

 divisions, with intervening transition series, thus : 



PKOTOZOIC ROCKS, OR NEW YORK SYSTEM. 



Transition Series. 1. Potsdam sandstone. 



f 2. Calciferous sandrock. 



I 3. Black River limestone. 

 First ok Lower Division. -{ 4. Trenton limestone. 



5. TJtica slate. 



6. Hudson River group. 



7. Oneida conglomerate. 

 Transition Series. •{ 8. Medina sandstone. 



9. Clinton group. 

 '10. Niagara group. 

 11. Onondaga salt group. 



Second OR Middle Division. .; JJ- ^at^'' ^'"^«^t°"^- ^^ , .„ ,, 



j 13. Pentamerus limestone, and Catskill slialy 



limestone. 



14. Oriskany sandstone. 



ri5. Caudigalli and Schoharie grits. 



Transition Scries. ■} 16. Onondaga limestone. 



17. Corniferous limestone. 



riS. Marcellus slate. 



Third or Upper Division. J JJ" Hamilton group. 



I zi). (jrenesee slate. 



(^21. Portage group. 

 Transition Series. 22. 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 in 

 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 with the description of the minor divisions in the 

 ascending order. 



Potsdam Saiidstone. — (No. 1 of Pennsylvania and Virginia 

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

 connecting link between the non-fossiliferous rocks below and the 

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

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



