236 GEOLOGY. 



Silurian ; but the vertebrates did not appear till the lat- 

 ter part of it, and then in small numbers, and only in the 

 low form of fishes. Reptiles did not appear till the lat- 

 ter part of the Devonian, the age of Fishes, and were not 

 in their greatest abundance till after the Palaeozoic time 

 was past. There were no Mammals in the Palaeozoic 

 ages. Many species of animals which flourished in those 

 ages, perhaps largely, at length vanished, never to ap- 

 pear again ; for it is a remarkable fact, that any species 

 which comes to an end is never again brought upon the 

 stage. For example, the Trilobites, of which there were 

 hundreds of species in the Silurian age, all dwindled 

 away one after another, till, in the Carboniferous age, the 

 last of the species disappeared, and none of all of them 

 has ever again been revived. At the close of the Car- 

 boniferous age, in the midst of the disturbances that oc- 

 curred, every species of animal and plant was destroyed, 

 though many species belonging to the same genera with 

 those of this age existed in the after ages. This uni- 

 versal destruction of the life of the Carboniferous age is 

 one of the great marks of distinction between this and 

 the following age. 



CHAPTER XVII. 



AGE OF EEPTILES. 



339. Names. We now pass from Palaeozoic to Meso- 

 zoic time, or the Mediaeval age of the earth, the age of 

 Reptiles. It is divided into three periods, the Triassic, 

 Jurassic, and Cretaceous. The Triassic is so called on 

 account of an obvious threefold division which the sys- 

 tem of rocks presents in Germany, though it is not seen 

 in other quarters of the world. The term Jurassic comes 

 from the Jura Mountains of Switzerland, where the for- 

 mation or system of strata designated by this name is 

 well developed, and has been particularly examined. 



