1892.] NATURAL SCIENCES OF PHILADELPHIA. 95 



in that case should have left its traces everywhere among all acces- 

 sible metamorphosed rocks. 



It has been suggested thai such future accession of carbonic acid 

 to the atmosphere diffused over a century or more, may be met and 

 counteracted by the consequent increased activity of tropical and 

 other vegetation. There is no doubt that as long as the earth con- 

 tinues otherwise fitted to sustain life, we may confidently expect 

 that in the future as in the past, new creatures will be evolved to 

 meet new physical conditions. But there is reason to believe that 

 vegetation, composed as it is of all existing individuals, has fully 

 adapted itself to present conditions including the actual quantity of 

 carbon dioxide heretofore and now being supplied from its own 

 dissolution and decay, and from such sources of natural supply as 

 the breath of animals, forest, prairie and accidental fires, volcanic 

 combustion, subterranean decomposition and others of the kind. 

 The amount of heat and moisture, the principal conditions of vege- 

 table life, is more likely to decline with the slow diminution of solar 

 vigor than to increase, and there is no reason for supposing that the 

 present rate of vegetable growth is in any degree limited or 

 restricted by the want of carbonic acid. If then the quantity, 

 already suflicient, continues to be daily augmented by the ever 

 increasing artificial combustion of coal, its entire absorption by 

 vegetation would require a new and distinct modification in vege- 

 table life. But any such adaptation must proceed in accordance 

 with fixed laws, which never halt or vary to save individuals or 

 species. On the contrary, their inexorable march even toward 

 higher forms involves the remorseless extinction not only of indi- 

 viduals but of whole species, genera and orders, an evolutionary 

 process which would doubtless have kept even pace with the slow 

 natural changes of environment, but hardly with the active inter- 

 ference of human intelligence possessing designs of its own in no 

 manner subordinated to the slow and gradual processes of natural 

 development. 



Similar considerations apply to the probable eflTect on animal life 

 of any considerable relative displacement of oxygen from the 

 atmosphere. We know that any — even the smallest — relative 

 increase of carbonic acid is injurious to the life-sustaining quality of 

 air, not necessarily on account of any actively poisonous qualities 

 of its own, but by its displacement or dilution of oxygen, and that 

 an atmosphere containing but eighteen per cent, by weight of 



