168 



CHARLES B. WAER1NG, M.A., PH.D., ON 



only a trace, scarcely 4 parts out of 10,000, while the oxygen 

 has increased to 2,300 out of the same amount. The ratio has 

 so changed from being only a fraction compared with the CO 2 , 

 that the oxygen to-day is almost 600 times the greater. At 

 no time is there evidence of a return to conditions once passed. 

 The tendency of gases is to diffuse themselves uniformly, 

 irrespective of their specific gravities. This process was aided 

 by aerial currents. There resulted from such action uniformity 

 of atmospheric composition over both land and sea, and in 

 all latitudes. To-day we see the same thing from the same 

 causes. 



During the same geological time changes were going on in 

 the water, changes whose biologic influence manifested them- 

 selves, or at least were accompanied by, changes of species in 

 the direction of those which now exist. The enormous deposits 

 of what, for lack of a better name, I may call organic lime- 

 stone and silicates, indicate waters once holding in solution 

 proportionally large amounts of lime and silica. These amounts 

 were greatest at first, and grew less and less as plants and 

 animals progressed in the work of making those insoluble 

 compounds in which so much has been stored away. The 

 amount of lime and silica held by the water was therefore 

 greatest in the Azoic time, grew less in the Eozoic, less yet in 

 the Silurian, less still in the Devonian, and so on down, each 

 period having less than the one before it ; until at last, probably 

 in the Quaternary, an equilibrium was reached by the inwash 

 from the land making good that which is removed by present 

 animal and vegetable action. 



The presence of these deposits in all latitudes indicates the 

 world-wide character of this process. Moreover the ocean 

 currents, tides and winds, tended to uniformity in the character 

 of the water everywhere. To-day, from local causes, some 

 parts of the ocean hold a larger percentage of mineral matter 

 than do some others, yet on the whole the great ocean is every- 

 where substantially the same, and probably such was the case 

 in each of the geological periods. 



The third biological factor is the soil. This affects directly 

 only vegetation, but indirectly all other forms of life. 



As soil is a compound of comminuted rock and vegetable 

 and animal matter, we may safely assume that, while before 

 the Eozoic the former was present as clay, sand, and gravel, 

 there was no soil. This beo;an to form after the other ingre- 

 dients had been washed upon the emerged land ; it increased 

 in quantity and improved in quality as time went on through 



