CHAPTER YI. 



SPECIES AND TIME. 



Two relations of species to time. — No evidence of past existence of minutely 

 graduated intermediate forms when such might be expected a priori. — 

 ijats, Pterodact}des, Dinosauria, and Birds. — Ichthyosajuria, Chelonia, 

 and Anoura, — Horse ancestry. — Labyrinthodonts and Trilobites. — Two 

 subdivisions of the second relation of species to time. — Sir "VVni. Thom- 

 son's views. — Probable period required for ultimate specific evolution 

 from primitive ancestral forms. — Geon)etrical increase of time required 

 for rapidly multiplying increase of structural differences. — Proboscis 

 monkey. — Time required for deposition of strata necessary for Dar- 

 winian evolution. — High organization of Silurian forms of life. — 

 Absence of fossils in oldest rocks. — Summary and conclusion. 



Two considerations present themselves with regard to the 

 necessary relation of species to time, if the theory of 

 '' Natural Selection ^' is valid and sufficient. 



The first is with regard to the evidences of the past 

 existence of intermediate forms, their duration and suc- 

 cession. 



The second is with regard to the total amount of time 

 required for the evolution of all organic forms from a few 

 original ones, and the bearing of other sciences on tiiis 

 question of time. 



As to the first consideration, evidence is as yet against 

 the modification of species by " Natural Selection ^ alone, 

 because not only are minutely transitional forms generally 



L 



