130 HISTORICAL GEOLOGY. 



The ages recognized are, then, Age of MollusJcs, or Silurian; Age 

 of Fishes, or Devonian; Carboniferous Age; Age of Meptiles; Age of Mam- 

 mals; Age of Man. 



Preceding these, there is the Azoic era, — the name being derived 

 from the Greek a and fan, life, and signifying the absence of life. 

 The Azoic rocks are mostly crystalline. 



The Silurian, Devonian, and Carboniferous ages naturally stand 

 somewhat apart from the following in the peculiar ancient forms of 

 the great portion of their living tribes, and to the whole collectively 

 the term Palaeozoic era is appropriately applied, — the word "palaeo- 

 zoic" being from the Greek izalaLoq, ancient, and faov. The following 

 age, or age of Keptiles, is correspondingly termed the Mesozoic, from 

 fieaoc, middle, and faov, it being the medieval era in geological history. 

 The Mammalian age is termed the Cenozoic, from aaivog, recent, and 

 faov. (The words Eocene, Miocene, etc., subdivisions of the age, are 

 in part from the same root.) 



The subdivisions of geological time are, then, — 

 I. Azoic Time or Age. 



II. Paleozoic Time. 



1. The Age of Mollusks, or Silurian. 



2. The Age of Fishes, or Devonian. 



3. The Age of Coal-Plants, or Carboniferous. 



III. Mesozoic Time. 



4. The Age of Keptiles. 



IV. Cenozoic Time. 



5. The Age of Mammals. 

 V. Era of Mind. 



6. The Age of Man. 



Subdivisions into Periods and Epochs. — The subdivisions under the ages, 

 the periods and epochs, vary, as has been said, in different countries. 

 The following table (fig. 134) presents a general view of those of 

 eastern North America, as far as the Palaeozoic is concerned, — the 

 Silurian, Devonian, and Carboniferous being well represented on the 

 North American continent. The rest of the series is from European 

 geology, in which the later ages are far better represented than in 

 America. In this manual, American geology is in general first con- 

 sidered, and afterwards such further illustrations are drawn from 

 other continents as are necessary for comprehensive views and 

 generalizations. Where America is deficient in its records, the 

 European are taken as the standard. 



The names of the periods and epochs for the Palaeozoic of Ame- 

 rica are the same that have been applied to the rocks by the New 

 York geologists. 



