

HISTORICAL GEOLOGY. 



139 



I. Arcelean Time. — The beginning, including a very long era 

 without life, and, finally, that in which appeared the earliest and 

 simplest forms of plants and animals. 



II. Silurian Age, or Age of Invertebrates. — The animal life 

 consisting distinctively of Invertebrates. 



III. Devonian Age, or Age of Fishes. — Fishes, a division of 

 Vertebrates (the earliest of which had appeared before the close of the 

 Silurian), the dominant race. 



IV. Carboniferous Age, or Age of Acrogens, and eminently 

 also the Age of Amphibians. — Characterized by Coal-plants, which 

 were chiefly of the tribe of Acrogens, — a tribe that then had its 

 grandest exhibition ; and in animal life, by the earlier Reptiles, be- 

 longing mostly to the lower division, Amphibians. 



V. Age of Reptiles. — Reptiles the dominant race. 



VI. Tertiary Age, or Age of Mammals. — Mammals the domi- 

 nant race. 



VII. Quaternary, or Age of Man. 



The general facts in the progress of life on the globe are illustrated 

 in the annexed diagram, — 



Age of Man, or Quater- 

 nary. 



Age of Mammals, or 

 Tertiary. 



Age of Reptiles, or Sec- 

 ondary. 



Carboniferous Age. 



Age of Fishes, or De- 

 vonian. 



Age of Invertebrates, or J 

 Silurian. 



Archaean Time. 



The horizontal bands represent the ages, in succession ; the vertical 

 correspond to different groups of animals and plants. The lower end 

 of each vertical band marks the point in geological time when, accord- 

 ing to present knowledge from fossils, the type it represents began ; 

 and the varying width in the same bands indicates the greater or less 

 expansion of the type. The following are accordingly the points the 

 diagram illustrates : — 



