LIFE ON THE EARTH. 137 



The same hypothesis applied to the formation of 

 the Coal Strata leads to very similar results. Higher 

 mean temperature, a greater quantity of moisture, 

 a larger dose of carbonic acid in the air, these things 

 must be allowed to have been active in accelerating 

 the growth of the plants in Palaeozoic ages. If it is 

 conceivable that the growth was then twice as rapid 

 as now, that only halves the immense period already 

 assigned by the calculation; and besides it takes 

 no account of the probably serious objection that 

 very rapid growth under these conditions would 

 be in some degree balanced by very rapid decay 

 and dissipation of the constituent elements of the 

 plants. 



From all that has been said we may learn that 

 by no hypothesis founded on probability, or consist- 

 ent even in a small degree with actual phenomena, 

 and the course of natural events, can we assign for 

 the deposition of the fossiliferous strata so short a 

 period as that last mentioned. It is rather to be 

 supposed very much longer, if reduction of tempe- 

 rature is to be taken as the mainly influential con- 

 dition of deviation from uniform action. For if this 

 reduction of temperature were taken at 20 it must 

 have required ages of ages to be accomplished by 

 the excess of radiation into space over the heat 

 received from the sun; the period may not elude 



