100 Evolution of the Earth. 



in the judgment of Professor Huxley, furnish an il- 

 lustration of the truth of the doctrine of biological evolu- 

 tion, which renders it as well established as is the Coper- 

 nican theory of the motions of the heavenly bodies. Beyond 

 the Eohippus, an animal with four toes and an aborted fifth 

 on its fore-feet, we have the Phenacodus,* a five-toed plan- 

 tigrade animal, which is regarded as the original progenitor 

 of the horse-family. The ancestors of the European horse, 

 which is supposed to have been introduced from Asia or 

 Northern Africa, have also been discovered in the Tertiary 

 deposits of the Eastern continents ; but the pedigree of the 

 horse is thus far most continuous in America. Strange to 

 say, the line of ancestry of the European horse, unlike that 

 of the American horse, has been traced back to the Palaeothe- 

 rium, also an ancestor of the tapir, and a connection of the 

 pachyderms. It becomes an interesting question for future 

 Palaeontologists, whether the horse has really arisen by in- 

 dependent lines of succession from two different stocks, or 

 whether his original home was not rather in America, 

 whence he or his ancestors passed to Asia through the Arc- 

 tic regions, when the two continents were united, and a mild- 

 er climate in the Polar regions permitted such migrations. 

 The development of this fruitful topic of the bearing of geo- 

 logical studies upon the question of biological evolution, 

 belongs rather to the treatment of the evolution of vegetal 

 and animal life. It is alluded to here merely to show how 

 palaeontology assists the geologist in accurately determin- 

 ing the order of geological succession, and corrects or sus- 

 tains his conclusions in regard to those changes in the 

 formation of continents and oceans, which have been going 

 on since the world began. 



It is proper for us to say here, however, that the succes- 

 sion of organic remains, in the geological strata, though not 

 complete, is, so far as discovered, precisely what it should 

 be to sustain the doctrine of organic evolution. The lowest 

 orders of archaic life have not been identified in the strat- 

 ified rocks ; they probably never will be. They were too 

 fragile — too easily destroyed by the operation of natural 

 agencies. The lowest remains which we find are those of 



* See " Origin of the Fittest," by Prof. E. D. Cope. A skeleton of the Phe- 

 nacoclus may be found in Prof. Cope's Collection, in Philadelphia. 



