280 SUDDEN A^PEAPwA^X'E OF Chap. IX, 



and as they would Ijc found embedded in sliglilly-different 

 sub-stages of the same formation, they would, according to 

 the principles followed l)y many paleontologists, be ranked 

 as new and distinct species. 



If, then, there be some degree of truth in these remarks, 

 we have no right to expect to find, in our geological for- 

 mations, an infinite number of those fine transitional forma 

 which, on our theor}', have connected all the past and present 

 species of the same gi-oup into one long and branching 

 chain of life. We ought only to look for a few links, and 

 such assuredly Ave do find — some more distantly, some more 

 closely, related to each other ; and these links, let them be 

 ever so close, if found in different stages of the same forma- 

 tion, would, by many paleontologists, be ranked as distinct 

 species. But I do not pretend that I should ever have suspect- 

 ed how poor was the record in the best preserved geologi- 

 cal sections, had not the absence of innumerable transitional 

 links between the species which lived at the commencement 

 and close of each formation, pressed so hardly on my theory. 



On the sudden Apjjearance of ichole Groups of allied 

 /Species. 



The abrupt manner in which Avhole groups of species 

 suddenly appear in certain formations, has been urged by 

 several paleontologists — for instance, by Agassiz, Pictet, and 

 Sedgwick — as a fatal objection to the belief in the trans- 

 mutation of species. If numerous species, belonging to the 

 same genera or families, have really started into life at 

 once, the fact would be fatal to the theory of descent with 

 slow modification through natural selection. For the devel- 

 opment of a group of forms, all of which have descended 

 from some one progenitor, nuist have been an extremely slow 

 process; and the progenitors must have lived long ages 

 before their mothfied descendants. But we continually over- 

 rate the perfection of the geological record and falsely infer, 

 because certain genera or families have not been foimd 

 beneath a certain stage, that they did not exist before that 

 stage. In all cases positive paleontological evidence may 

 be implicitly trusted ; negative evidence is worthless, as 

 experience has so often sho"wn. We continually forget how 

 large the world is, compared with the area over which our 

 geological formations have been carefully examined ; we 



