CHAPTER XIII. 

 THE ORIGIN OF THE GREAT CLASSES. 



The origin of the great classes of the vegetable and 

 animal kingdom is a historical problem in which geo- 

 logy has the first word. 



The most important facts geology teaches us are : 

 istly. that the origin of the different classes Ues very 



far back. 

 2dly. that a new class appears suddenly with a great 

 many, mostly highly differentiated, different 

 forms. 

 3dly. that the further we get away from the birth of 

 the class, the more the number of different 

 forms diminishes, and the more „reduced" these 

 become. 

 We will illustrate these important facts by some 

 examples. 



Scott says (p. 6. of the Introduction to his study in 

 fossil Botany 1908) about the very ancient origin of the 

 great divisions: 



„There are probably no biologists left now who 

 „oppose in toto the doctrine of evolution, but if there 

 „were, they might draw a telling, though fallacious 

 „argument from the high organization of the Devonian 

 „flora". 



The sudden appearance in a large number of diffe- 

 rent forms, of such groups as the Reptils, Cycadoph5^es 



