GEOLOGIC CLIMATES 257 



of the carbon dioxide makes the air more transparent to reflected heat, 

 the blanket is thinner, the temperature falls, the moisture decreases, and 

 areal or zonal differences of climate are intensified, because the obliquity 

 of the sun's rays becomes a greater proportionate factor. 



Extreme and rapid climatic changes can not occur for the reason 

 that causes act slowly, while effects lag, and counterbalancing factors as 

 checks come into play. One of these checks is the ocean, which serves 

 as a great reservoir of carbon dioxide, containing some eighteen times 

 as much as the atmosphere. On depletion of the atmospheric carbon 

 dioxide the ocean by diffusion gives up some of its supply, and thus 

 helps to bring back the normal balance. 



If this theory of climate be true, it will harmonize with geologic facts. 

 Let us make a tentative application. The great land elevation and ex- 

 pansion, with mountain formation, of Tertiary time was accompanied, 

 at least in the earlier periods, by warm climate even in the arctic region ; 

 but it was followed by Pleistocene glaciation. The very remarkable 

 glaciation found in Permo-Carboniferous strata of middle and southern 

 latitudes followed the land expansion of the later Paleozoic and the for- 

 mation of the Carboniferous coals. These two series of events seem 

 quite clear. If other epochs of glaciation are found, we may expect 

 that they will have succeeded eras of broad expansion of new lands or 

 other causes of carbon dioxide depletion. Seasons of aridity, with pos- 

 sible production of salinas, are also the effects of impoverishment of the 

 atmosphere in carbon dioxide and moisture in less degree, perhaps, than 

 required for glaciation ; but aridity will usually accompany glaciation, 

 since both classes of phenomena imply unequal distribution of precipi- 

 tation. Prevailing red color of the rock strata may also indicate com- 

 parative aridity. Seasons of warmth and moisture, with luxuriant plant 

 life, should be found to follow eras of transgression by the sea and qui- 

 escent conditions. Professor Chamberlin has shown how submergence 

 of the continental borders favors limestone accumulations, which in 

 turn causes enrichment of the ocean and air in carbon dioxide, since 

 the limestone fixes only one equivalent of the carbon dioxide and re- 

 leases one to the water from the bicarbonate held in solution. For 

 example, the warm and probably moist climate so widespread in the 

 mid-Carboniferous followed the long submergence and limestone-making 

 of the Subcarboniferous ; and that of the Tertiary succeeded the lime- 

 stone deposition of the Mesozoic and Eocene. 



If the salt deposits of the Cambrian and later time are evaporation 

 products, then certainly the atmosphere of those early times did not con- 

 tain the carbon dioxide which has been stored in the later strata. These 

 two sets of facts, the vast quantities of stored carbon and the ancient 



