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SCIENCE. 



[N. S. Vol. VIII. No. 193. 



and of the present Central American region, 

 we can realize as never before the imme- 

 diate effect of a simple though very decided 

 change of climate on organic life. 



As a result of the submergence of the land 

 in the north Atlantic and Arctic regions 

 during the Leda or Champlain epoch suc- 

 ceeding, and the consequent amelioration of 

 the climate, there was a return of a por- 

 tion of the Pliocene species to the vast area 

 thus freed from the presence of land ice. 



Another effect of change of climate due to 

 the further upheaval, drainage and drying 

 up of lakes and river sources in the central 

 portions of all the continents was the de- 

 struction of forests resulting from the drying- 

 up of the lakes and streams, the formation of 

 vast internal desert regions, with the desert 

 floras and fauna and saline animals peculiar 

 to them ; these are the last steps in geologi- 

 cal history of the origination of species, and 

 have been taken almost under the observa- 

 tion of man. In the origin of species adap- 

 ted to desert areas and to salt lakes, fauna 

 relictce of the lakes on the elevated plains 

 of Asia, South America, Africa, Sweden and 

 the Great Lake region, we see that geo- 

 graphical isolation and the absence of com- 

 petition are the primary factors in the 

 case. 



In conclusion, it is, from the nature of 

 the case, notwithstanding the imperfection 

 of the geological record, apparent that the 

 fullest, most complete and convincing proof 

 of organic evolution is derived from the 

 past history of life, from paleontology, which 

 involves the fact of geological succession. 

 Looking back for half a century we see that 

 organic evolution is a fact and is grounded 

 and dependent on geological evolution, and 

 the latter on cosmical evolution. Should 

 we ever have to abandon the principle of 

 evolution we should also have to give up the 

 theory of gravitation, the principle of the cor- 

 relation of physical forces, and also the con- 

 ception of the unity of nature. All of these 



principles are interdependent, and form the 

 foundation stones of our modern science. 



The rapid summary we have given of the 

 successive changes and revolutions in the 

 earth's history and the fact that they are 

 accompanied or followed by the process of 

 the extinction of the unadapted, and their 

 replacement by the more specialized and 

 better adapted, show that there is between 

 these two sets of phenomena a relation of 

 cause and effect. 



Moreover, it cannot be denied that the 

 formation of our solar system in the man- 

 ner outlined by the founders of the nebu- 

 lar hypothesis, that the progressive changes 

 in geology and the earth's topography, the 

 gradual building-up or evolution of the con- 

 tinents, and the increasing fitness and in- 

 telligence of the life on its surface, the final 

 outcome being man, whose physical devel- 

 opment was practically completed at the 

 beginning of the Quaternary period, and 

 whose intellectual and moral improvement 

 have, as it were, but just begun— the sci- 

 entist, as such, can scarcely deny that this 

 process of evolution, along so many lines 

 and involving not only material but mental 

 and moral advances, has gone on in an 

 orderly and progressive way. The impres- 

 sion left on the mind is that all these 

 changes, inorganic and organic, have been 

 purposive rather than fortuitous, the result 

 of the action of natural laws, impressed on 

 matter by an Intelligence and force outside 

 of, but yet immanent in, all things material. 



"With Hutton, we may say: "We have now 

 got to the end of our reasoning ; we have no 

 data further to conclude immediately from 

 that which actually is. Bat we have got 

 enough— we have the satisfaction to find 

 that in Nature there is wisdom, system 

 and consistency." 



Here, as men of science merely, we may 

 pause and confess our ignorance of the first 

 or ultimate cause of this progressive evolu- 

 tionary movement pervading the material 



