DISTRIBUTION 165 



II. Paleozoic Era. 



1. Cambrian. 4. Carboniferous. 



2. Silurian. 5. Permian. 



3. Devonian. 



Tlie oldest paleozoic period, the Cambrian, contains only invertebrate 

 fossils: silicious sponges, the problematical graptolites, medusae, trilobites, 

 gigantostraca, cystoids, holothurians, brachiopods, nautiloids, gasteropods, and 

 a few lamellibranchs. Trilobites, cystoids, gigantostraca, and the blastoids 

 and tetracoralla, which appear in the Silurian, reach their culmination and 

 become extinct in the paleozoic. Fishes appear in the Silurian, and acquire a 

 great development in the Devonian. The earliest Amphibia and reptiles come 

 from the carboniferous. 



III. IMesozoic Era. 



I. Triassic. 2. Jurassic. 3. Cretaceous. 



The mesozoic era was the age of reptiles, which were represented by numer- 

 ous forms, some of gigantic size; most of them becoming extinct in the creta- 

 ceous. The first mammals appear in the triassic, the birds in the Jurassic. 

 Among the invertebrates the ammonites, which appeared in the Devonian, 

 reached their greatest development and became extinct in this era. 



IV. Cenozoic Era. 



(a) Tertiary. 



1. Eocene. 3. Miocene. 



2. Oligocene. 4. Pliocene. 

 (6) Quaternary. 



5. Pleistocene (Ice Age, Diluvium). 6. Recent. 



In the tertiary all of the now living orders of mammals and birds appeared, 

 among them probably man, whose remains have been traced with certainty to 

 the pleistocene. 



