CLIMATE AND CARBONIC ACID. 251 



change be from warm to cold, cooling waters tighten their grasp on the 

 precious gas that might offset the atmospheric depletion. If they be 

 warmed beneath an air growing rich in carbon dioxide, they become 

 generous of their hoard. The processes are, therefore, auxiliary and 

 intensifying, not initiative. 



For the initiative process, which may start the train of effects lead- 

 ing to atmospheric enrichment and a warm epoch, we must refer again 

 to the periodic rest and unrest of the earth's forces. 



When, through adjustment of the relations between continental 

 masses and masses beneath the oceans, the internal stresses of the globe 

 have been balanced, the average elevation of lands above sea level is a 

 maximum. The highest rate of consumption of carbon dioxide by 

 weathering may be assumed to follow after a brief but appreciable in- 

 terval, and from that time forth to diminish. As heights waste and 

 slopes sink low, they become mantled with the residual product of 

 weathering, soil, and efficient contact of carbon dioxide with unaltered 

 rock is limited. When the average height of land is become that of 

 a low plain, carbonation is reduced to a very small part of its maximum 

 activity, and the rate of consumption is slow. At some stage of this 

 change the diminishing rate of depletion may equal and thereafter sink 

 below the rate of supply. Thus the initial condition of a return of 

 milder climate inheres in the transient nature of the cause of a cold 

 epoch. The result might, however, be long delayed, but for the acceler- 

 ating influence of auxiliary processes, of which, as already stated, life is 

 believed to be the most potent. 



It is a recorded fact of geologic history that periods of minimum 

 continental elevation have been periods of extensive marine expansion. 

 These conditions have been associated with remarkable development 

 of marine faunas and with general mildness. Chamberlin was the first 

 to point out a causal relation between these conditions and effects. He 

 entertains the idea that at the climax of an epoch of crustal adjustment, 

 the elevation of continents may be somewhat greater than that required 

 by radial equilibrium. If so, they should in time exhibit a tendency to 

 settle back. In so far as this period of readjustment of balance might 

 suffice for deep general denudation, the subsiding lands would present 

 low plain surfaces to the sea. These conditions would be most favor- 

 able for wide migration of the shore from the continental margins far 

 inland, and would result in extensive areas of relatively shallow water. 

 A fauna, which had existed on the narrow slope between the original 

 position of the shore and an oceanic basin, would find its habitat 

 immensely enlarged and favorably conditioned. Eesponding, it would 

 develop varieties, species and genera until, as sometimes was the case, 

 exuberance ran into unfitness and decadence. 



The lowland aspect of continents would be favorable to other 



