CHAPTER VIII 



THE SILURIAN (UPPER SILURIAN) PERIOD 

 Origin of Name, Subdivisions, etc. 



We have already learned how the great body of lowest fossil- 

 iferous strata in the British Isles was called the Silurian system by 

 Murchison in 1835. The name was derived from Silures, an old 

 tribe which once lived in part of Wales. In the preceding chapter 

 we have also shown how the Silurian has since been divided into 

 three systems — Cambrian, Ordovician, and Silurian. In view of 

 the priority of Murchison's term " Silurian," and the fact that the 

 Ordovician strata are now known to be more important and wide- 

 spread than those we call Silurian, it seems inappropriate that 

 the terms Ordovician and Silurian are not employed in the reverse 

 order. 



Since the Silurian strata, too, were first carefully studied in 

 New York, the section for that state becomes to a very considerable 

 degree a standard of comparison for all American Silurian strata. 

 Like the Cambrian and Ordovician systems, the Silurian is gener- 

 ally subdivided into three major portions or series, these in turn 

 being subdivided into various stages. The most recent classi- 

 fication by the New York Geological Survey is as follows: 



[ Manlius limestone. 

 Rondout waterlime. 

 < Cobleskill limestone. 



I Salina shale, salt, and waterlime (also the 

 { Shawangunk conglomerate). 

 f Guelph dolomite 

 J Lockport dolomite 

 i Clinton shale, limestone, sandstone, and iron 



Silurian 



System 



Cayugan series 

 (Upper Silurian) 



Niagaran series 

 (Middle Silurian) 



Oswegan series 

 (Lower Silurian) 



Niagara limestone. 



f Medina and Oneida sandstone, conglomer- 

 \ ate, and shale. 

 [ Oswego sandstone. 



The New York Silurian section is more complete than the 

 Ordovician, because the unconformities are fewer and of lesser 



103 



