SUBDIVISIONS IN THE HISTORY. 129 



The Articulates, as the table shows, commence in the Silurian 

 (as Crustaceans and Worms), and continue expanding in numbers 

 and grade to the present time. 



Fishes begin in the Silurian, are very abundant in the Devonian, 

 and continue on, becoming increasingly diversified to the last, with- 

 out much rise in grade. 



Reptiles begin in the top of the Devonian, and reach their maxi- 

 mum in the Reptilian age. 



Mammals begin in the Reptilian age, and have their maximum in 

 the Mammalian age. 



As to Plants, Sea-weeds (or Algce) are the earliest of the globe, pro- 

 bably preceding animal life. The Acrogens begin in the Devonian, 

 or earlier, and have their greatest expansion in the age of Coal- 

 Plants, where they occur with abundant Conifers. Cycads begin 

 in the Carboniferous, and have their greatest expansion in the Rep- 

 tilian age. Dicotyledons begin in the closing period of the Reptilian 

 age, and expand, along with Palms, through the age of Mammals. 



The Silurian is eminently the age of Mollusks ; for this is the 

 highest branch of the animal kingdom which is represented at that 

 time in all its grand subdivisions. Brachiopods, Conchifers, Gas- 

 teropods, Pteropods, Cephalopods, begin in the Lower Silurian, and 

 the Molluscan type is thus unfolded at the outset, while the Articu- 

 lates are represented by only the inferior marine divisions, and the 

 Radiates, besides being an inferior type, are present only in the 

 lower tribes of its three classes. The age is eminently, therefore, 

 the age of Mollusks. Any fishes discovered in the Silurian would 

 foreshadow, in the manner explained, the age of Fishes, as the 

 Reptiles of the Carboniferous age foreshadowed the Reptilian age, 

 and the Mammals of the age of Reptiles the Mammalian age. 



In the Devonian age, the Fishes, the lowest of Vertebrates, are 

 the dominant type. The Reptilian age is still more eminently an 

 age of Reptiles, and the Mammalian age an age of Mammals, as is 

 shown beyond in the survey of these ages. 



On botanical data, the ages would he— first, the age of Sea-weeds, 

 covering the ages of Mollusks and Fishes ; second, the age of Coal- 

 Plants or Acrogens, or the Carboniferous age ; third, the age of Cycads, 

 corresponding to the age of Reptiles ; and, fourth, the age of Palms 

 and Dicotyledons, corresponding to the Mammalian age. The only 

 addition to the preceding divisions based on the animal tribes 

 which is thence suggested by the vegetable kingdom is the Carboni- 

 ferous. In the zoological series this might be called the age of Am- 

 phibians, as it is characterized prominently by the amphibian division 

 of Reptiles. 



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