104 EVOLUTION AND DOGMA. 



Considering the relations to each other of only 

 existing species, De Candolle felt obliged to curtail 

 greatly the number of species of the genus quercus, 

 but when the genealogy of the oak is studied in the 

 light of geology and paleontology, it is found that it 

 originated far back in the Cretaceous Period, and 

 that this ancient geologic form is undoubtedly the 

 common ancestor of all the species and varieties now 

 existing. For we have it on the testimony of such 

 a competent witness as Lesquereux, that not only 

 the oak but all " the essential types of our actual 

 flora are marked in the Cretaceous Period, and have 

 come to us, after passing without notable changes 

 through the Tertiary formations of our conti- 

 nent." 



Baird's researches upon the birds of North Amer- 

 ica, admirably corroborate De Candolle's induction, 

 to wit: "That when a large number of specimens 

 from a sufficiently extensive territory are examined 

 and compared, it is found that what are ordinarily 

 regarded as quite distinct species are often no more 

 than races and varieties, or what evolutionists would 

 denominate incipient species. For along the border- 

 ing lines of the habitats of such species, it is observed 

 that the specific characters of the divers forms are so 

 blended that it is often difficult, if not impossible, to 

 distinguish one species from another. Indeed, 

 whether the birds observed in such cases belong to 

 the same or to different species will depend, mainly 

 or entirely, either on the naturalist's point of view, 

 or on the number of intermediate forms which he 

 may be able to collect and compare." 



