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. 
NS, 
3 | 
Fic. 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 paleontology; 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 crit’cs 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 
