558 F. H. KNOWLTOX EVOLUTIOX OF GEOLOGIC CLIMATES 



in the atmosphere and in the sea is reestablished. Hence a reduction of car- 

 bonic acid in the air is automatically followed by the discharge of nearly as 

 large a quantity from the sea, so that any reduction is distributed between 

 the air and the ocean. Any increase of carbonic acid in the atmosphere is 

 followed by a reverse change, and only one-sixth of the amount poured into 

 the atmosphere is retained there. It is true that great variations in the rela- 

 tive extent of sea and land would affect the dissociation pressure of the bicar- 

 bonates in the sea ; but it would require a great reduction in the area of the 

 sea surface to affect the equilibrium appreciably." 



Again^ it is to be pointed out that there is a iion-coincideiice of date>s 

 for periods of glacial activities. In accordance with the well-known law 

 of diffusion of gases^ an}- variation of the carbon-dioxide content of the 

 atmosphere should affect the temperature of the whole world simul- 

 taneousl}', although, as shown by Arrhenius, it need not be the same in 

 all latitudes ; but it might be expected that corresponding latitudes in th..^ 

 hemispheres would exhibit practically the same effects. But the facts 

 of historical geology do not altogether substantiate this supposition. 

 Another weighty objection is offered by the fact that certain conditions 

 that might have been expected to influence the variation of carbon- 

 dioxide in the atmosphere have not been followed by the glacial activity 

 the theory would call for. For instance, those periods of active con- 

 sumption of carbon-dioxide, as marked by the formation of great lime- 

 stone deposits, must have been supplied from the atmosphere. Among 

 the greatest limestone-producing periods are the Mississippian, Jurassic, 

 Cretaceous, and Eocene ; yet none of these was followed by glacial mani- 

 festations. The Miocene and Pliocene, which were followed by pro- 

 nounced glaciation, have far less of known limestone or coal accumula- 

 tion than the Pennsylvanian or Cretaceous, both of which are without 

 glacial activities. 



Periods of intensive vulcanism, such as occurred in the Devonian, the 

 Permian, the Upper Cretaceous, the Eocene, and the Oligocene, were 

 not followed by marked glacial activity; yet the "Permo-Carboniferous'^ 

 and Pleistocene glacial epochs were preceded by vulcanism. 



The conclusion, therefore, seems to me unavoidable that the hypothesis 

 postulated on an increase or decrease of the amount of carbon-dioxide 

 in the atmosphere can not be regarded as a major factor in controlling 

 glaciation. That it may have at times been a minor contributing factor 

 is not only possible but quite probable. 



Transportation theory. — In attempting to account for the presence of 

 the great variety of plant remains now found in Arctic and sub-Arctic 

 regions, it has been boldly asserted by some writers that they have beec 



