94 PR0CEEDINC4S OF THE ACADEMY OF [1892. 



evolution of higher forms, so the converse process, though to a less 

 extent — since all coal is not accessible to the destructive power of 

 raan — must tend to restore the atmosphere to its precarboniferous 

 condition and to some extent, however minute, impair or restrict its 

 capacity for sustaining the higher forms of animal life as now 

 constituted. 



The data and proportions supplied in the table may of course be 

 applied to such assumption of absolute quantities as may best satisfy 

 individual minds. But its proportions are correct, and on any 

 supposition it furnishes proof that some amount of deleterious 

 influence must be exerted on the atmosphere, and therefore on the 

 physical constitution and qualities of all air breathing animals and 

 especially on the higher forms, which, being most specialized, are the 

 least adaptable. 



If it be objected that it is not to be accepted without specific 

 proof that all of this carbon dioxide was at any one time in atmos- 

 pheric suspension, then we have to suppose some agency of constant 

 and steady supply during the enormous vegetable demand of the 

 prolonged carboniferous i^eriod. This agency could only have 

 been a vast and long continued amount of internal heat either dif- 

 fused by steam, or occurring sufficiently near the surface to permit 

 egress. Such heat would have been necessary to expel it from the 

 carbonates in which it had been previously fixed, and must have 

 been at the same time sufficiently intense to fuse and decompose 

 limestone, and yet of a character consistent with the most profuse 

 vegetable growth that has at any period occurred on the earth. 



Nevertheless the suggestion is not beyond the bounds of possi- 

 bility. Large quantities of carbon dioxide have always been, and 

 now are being constantly emitted from the deep recesses of the 

 earth's mass and constitute an essential part of the existing con- 

 ditions of respiration ; and it may be conceded that such dissolution 

 of carbonates and evolution of carbon dioxide may have prevailed 

 to a greater extent than at present before the earth's crust had 

 cooled at all points to present temperatures, and may have aided the 

 supply furnished from the atmosphere. But tliat the process was 

 sufficient of itself to account for the great quantities that were fixed 

 in the coal beds during the carboniferous period is not credible, be- 

 cause not supported either by the comparative absence of such pro- 

 cess before and after that period, or by such amount of evidence as 



