CHAPTER XXIV 



THE SILURIAN (UPPER SILURIAN) PERIOD 



The name Silurian, like Cambrian and Ordovician, refers to 

 Wales. The term was proposed by Murchison in 1835 f° r a g re at 

 system of strata older than the Devonian, and was taken from the 

 Siiures, another ancient tribe of Britons which inhabited part of 

 Wales. Murchison gave great extension to his Silurian system, 

 including in it most of Sedgwick's Cambrian, but, as already pointed 

 out, the present tendency is to divide this vast succession of rocks 

 into three systems of equivalent rank. It is unfortunate, and even 

 unjust, that Murchison's term should not have been retained for 

 the more important and widely developed lower division, now 

 called the Ordovician, rather than for the upper division. 



As in the Ordovician and Devonian, the New York classification, 

 given in tabular form below, is the standard of reference for the 

 American Silurian. 



3. Upper Pentamerus Stage. 

 2. Shaly Limestone Stage. 

 Sil ur ian { ^ Lower Pentamerus Stage. 



System. 2 - Onondaga Series. Salina and Water-lime beds. 



Niagara Stage. 

 Niagara Series. <! 2. Clinton Stage. 



Lower Helderberg 

 Series. 



1. Medina Stage. 



American. — The disturbance which closed the Ordovician does 

 not appear to have materially enlarged the extent of the con- 

 tinent, and at the beginning of the Silurian the general disposition 

 of land and water was much what it had been before. A narrow 

 strip of coast lands had been added to the shore of the northern 

 pre-Cambrian land mass, converting Minnesota, Wisconsin, much 

 of the province of Ontario, northern New York, and New Jersey, 

 2 c 385 



