Paleontology. 165 



ture and in the interaction of its correlated parts. The whole 

 process and its result is roughly represented in the accompanying 

 diagram, in which A B represents the course of geological time, 

 and the curve, the rise, culmination, and decline of successive 

 dominant classes. 



FIG. 59. Diagram of Geological Succession of the Classes of the 

 Animal Kingdom. (After Le Conte.) 



I will here leave the evidence which is thus yielded 

 by the most general principles that have been esta- 

 blished by the science of palaeontology ; and I will 

 devote the rest of this chapter to a detailed con- 

 sideration of a few highly special lines of evidence. 

 By thus suddenly passing from one extreme to the 

 other, I hope to convey the best idea that can be 

 conveyed within a brief compass of the minuteness, as 

 well as the extent, of the testimony which is furnished 

 by the rocks. 



When Darwin first published his Origin of Species, 

 adverse critics fastened upon the " missing-link " argu- 

 ment as the strongest that they could bring against 

 the theory of descent. Although Darwin had himself 

 strongly insisted on the imperfection of the geological 

 record, and the consequent precariousness of any ne- 

 gative conclusions raised upon it, these critics main- 

 tained that he was making too great a demand upon the 

 argument from ignorance that, even allowing for the 

 imperfection of the record, they would certainly have 

 expected at least a few cases of testimony to specific 

 transmutation. For, they urged in effect, looking to 



