EFFECTS REFEEEED TO THEIE CAUSES. 763 



3. Through convection from masses or dikes of fused rock into the adjoining rocks. 



3. Chemical change, p- 698. 



4. The Sun, p. 697. 



XIII. Secular Variations in Climate. 



1. Through change in amount of heat given out by the sun, p. 697. 



2. Through the escape outward of the earth's interior heat, p. 699. 



3. Through a secular change in the density of the atmosphere, that is in the amount 

 of carbonic acid, moisture, etc., p. 697. 



4. Through changes in the amount, position, and height of lands over the earth, 

 pp. 44, 541. 



5. Through changes in the courses of oceanic currents, pp. 541, 755. 



6. Through variations in the eccentricity of the earth's orbit, p. 697. 



XIV. Origin of Continents and Oceanic Basins. 

 Page 738. 



XV. Extinction of Species. 



The ordinary effects of nearly all the following causes of extinction are simply 

 destruction of life. But they may also occasion extinction of species. 



I. Catastrophic Causes, not Climated. 



I. Through the emergence of a region, with its aquatic life. 



2- Through the submergence of a region, with its terrestrial life. 



3. Through a change in the level of wave action, or in the relations of a sea to 

 currents, these bearing detritus or not. 



4. Through a change of salt-water seas or lagoons to fresh-water, and the reverse, 

 p. 610. 



5. Through the partial or complete evaporation of salt-water seas or lagoons. 



6. Through earthquake-waves. 



7. Through the heating of the ocean's waters hy means of extensive igneous erup- 

 tions, or through the flooding the land by such eruptions; effectual for volcanic islands, 

 but hardly for wide continental or oceanic areas. 



II. Climated Causes. 



8. Through the change of level of an emerged region, changing its climate as to its 

 range of temperature, moisture, etc., or as to the excesses of that range. 



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 to the cold or 

 warm oceanic currents, and affecting thus oceanic temperature, and also the temper- 

 ature of atmospheric currents. 



II. Through terrestial or cosmical changes, occasioning an era of great cold for a 

 hemisphere, or for both hemispheres, thereb} r giving greater cold to oceanic as well 

 as to atmospheric currents, p. 488. 



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. 



