557 



CHAPTER XXIII. 



THE UPPER SILURIAN. 



UPPER SILURIAN OF NOVA SCOTIA OF NEW BRUNSWICK USEFUL MIN- 

 ERALS FOSSIL REAIAINS METAMORPHISM OF SEDIMENTS IGNEOUS 



ROCKS. 



That enormous mass of sediments constituting the Silurian system 

 of Sir Roderick Murcliison, is by some geologists divided into three 

 portions — the Upper, Middle, and Lower. As will be seen, however, 

 by reference to the table of geological cycles on p. 137, in North 

 America this great system of formations represents tivo entire 

 geological cycles, and no more. One of these has been named the 

 Upper and the other the Lower Silurian ; tliough, in accordance with 

 ordinary geological nomenclature, each of these great groups, co- 

 ordinate in importance with the Devonian and Carboniferous, might 

 have a distinct name. The illustrious author of " Siluria " has not, 

 in his latest edition (1867), claimed for the Silurian rocks this dis- 

 tinction of constituting two systems ; but he has recognised the term 

 Primordial, proposed by Barrande, in so far as to designate the lowest 

 members of the system as " Primordial Silurian." While, however, 

 the term Silurian as thus held includes two great cycles of the earth's 

 history, the term Primordial is to be understood in a limited sense, 

 since the only truly Pi'imordial rocks arc the Laurentian, or those 

 still older sediments from which the materials of the Laurentian have 

 been in part derived. 



Acadia cannot, however, claim to be a typical region for any of 

 these series of rocks, presenting them but in limited areas, and so 

 much altered and disturbed, that their arrangement and subdivisions 

 are by no means so clear as in tlie great inland i)laiiis of North America. 

 We may therefore in this work rest content Avith tlie present nomen- 

 clature, and proceed to consider the Upper Silurian as developed in 

 Nova Scotia and New Brunswick. 



