36 The Ma\e'Up and the Wordings of the Earth 



amphibians appeared before reptiles, reptiles appeared before 

 birds, birds appeared before mammals. These facts do not 

 show that one class gave rise to the next ** higher " class in 

 this order. They do show that at successive periods there 

 appeared upon the earth more and more highly specialized 

 types of animals. 



Fig. 4. OSTRACODERMS 



Small armored fishes from the lower Devonian o£ Europe, 

 remains. After Koken. 



Restored from fossil 



The appearance of new forms of plant life at successive 

 levels also followed a progression from those that we con- 

 sider lower to those that we class as higher. Vegetation seems 

 to have been at its rankest during the period in which the 

 material for our coal beds was growing (Fig. 5). The 

 conditions under which these plants grew can be com- 

 pared to some of the present-day tropical swamps. True 



