THE TERTIARY PERIOD 



311 



river gravels, which are often capped by lava. The famous gold 

 deposits of Cripple Creek, Colorado, and Tonopah, Nevada, and 

 the copper deposits of Butte, Montana, all occur as veins in, or 

 adjacent to, Tertiary igneous rocks. 



Valuable phosphate deposits occur in the Tertiary limestones 

 of Florida. 



Life of the Tektiary 



Taken as a whole, the life of the Cenozoic era was markedly 

 different from that of the Mesozoic. Even in the Tertiary period 

 the most important groups of plants and animals had a decidedly 

 modern aspect. Most of the plants and the invertebrate animals 

 of the Tertiary period belonged to genera which still exist, while 

 the present-day species gradually increased from a small percentage 

 in the Eocene to a large percentage in the Pliocene. Among the 

 Vertebrates, the Fishes, Amphibians, Reptiles, 1 and Birds differed 

 but little from those of today. The Mam- 

 mals, however, which were small, primitive, 

 and relatively rare throughout the Mesozoic, 

 showed a wonderful development both in 

 number of individuals and diversity of forms. 

 The Mammals are, therefore, the most in- 

 teresting and characteristic organisms of 

 Tertiary time. 



Plants 



Vegetation had assumed a pretty dis- 

 tinctly modern aspect well before the open- 

 ing of the Cenozoic era, the great revolution 

 from ancient to modern types having taken 

 place about the middle of the Mesozoic era. 

 During the Tertiary, however, there was 

 notable progress toward even more modern 

 conditions, so that many genera became the same as now and grad- 

 ually more and more present-day species were introduced. 



Among the simplest or single-celled plants, the Diatoms deserve 

 special mention. In certain times and places they swarmed in the 



1 Recently a few Dinosaur remains have been found in the earliest Ter- 

 tiary rocks, but otherwise all of the characteristic Mesozoic Reptiles had 

 become extinct, leaving representatives only of such modern groups as Liz- 

 ards, Snakes, Turtles, Crocodiles, and a few other water forms. 



Fig. 190 

 Diatoms from diato- 

 maceous earth of Ter- 

 tiary age. Greatly en- 

 larged. 



