XIII THE GEOLOGICAL EVIDENCES OF EA'OLVTIOX 409 



exhibits a steady progression from lower to higher types, 

 excepting only the deiiciency in the bird record which is 

 easily explained. The comparative i^erfection of type in 

 which each of these classes first ap2:>ears, renders it certain that 

 the origin of each and all of them must be sought much 

 farther back than any records which have yet been discovered. 

 The researches of palaeontologists and embryologists indicate 

 a reptilian origin for birds and mammals, while reptiles and 

 amphibia arose, perhaps independently, from fishes. 



Concluding BemarJcs. 



The brief reWew we have now taken of the more suggestive 

 facts presented by the geological succession of organic forms, 

 is sufficient to show that most, if not all, of the supposed 

 difficulties which it j^resents in the way of evolution, are due 

 either to imperfections in the geological record itself, or to our 

 still very incomplete knowledge of Avhat is really recorded in 

 the earth's crust. AVe learn, however, that just as discovery 

 progresses, gaps are filled up and difficulties disappear ; while, 

 in the case of many individual groups, we have already 

 obtained all the evidence of progressive development that can 

 reasonably be expected. AVe conclude, therefore, that the 

 geological difficulty has now disappeared ; and that this noble 

 science, when properly understood, aflfords clear and weighty 

 evidence of evolution. 



