844 



EFFECTS REFERRED TO THEIR CAUSES. 



9. Through the change of level of a submerged oceanic region, changing thereby 

 its relations to warm and cold oceanic currents. 



10. Through changes of level in the land, giving a changed direction tc the cold or 

 warm oceanic currents, and affecting thus oceanic temperature, and also „he temper- 

 ature of atmospheric currents. 



11. Through terrestial or cosmical changes, occasioning an era of gre»t cold for a 

 hemisphere, or for both hemispheres, thereby giving greater cold to oceanic as well 

 as to atmospheric currents, p. 715. 



11. Through climatal excesses as to heat and cold, moisture and drought, such as 

 occur, under unchanged conditions of level, once or so in a century. 



13. Through the gradual change of climate over the globe, consequent on the earth's 

 secular refrigeration. 



III. Causes of Extinction depending on the Mutual Relations of Species. 



14. Through a loss of the proper food, occasioned by destructions of species, accord- 

 ing to any of the above or other methods. 



15. Through the excessive multiplication of the natural enemies of the individuals 

 of any species. 



16. Through the excessive multiplication of individuals of a species, so that food fails 

 and famine ensues. 



These and other related causes have been ably discussed by Darwin. 



IV. Causes of Extinction depending on the Successional Relations of Species. 



17. Through whatever means — the above or others — that may have sufficed, with 

 the lapse of time, to produce changes in the specific characters of species : in other 

 words, through progress in the evolution — however carried forward — of the systems 

 of lif«. 





