THE PERMIAN PERIOD. 669 



With these conditioning influences and liabilities in mind, we may resume the 

 sequences of the Permian deformation. 



i. Interruption of the water-heating system. — The first effect, as already 

 noted, must have been a serious interruption of the free polar circulation that 

 had previously prevailed, and which has long been confidently regarded as one 

 of the greatest of the agencies that maintained the previous mild temperature 

 in those regions. In the Southern Hemisphere, the distribution of life furnishes 

 special reasons for believing that the land was appreciably more extensive, and 

 more completely connected, than it is at the present day, and geologists, quite 

 without reference to any climatic effects, have postulated such connections. 

 A migrating tract for land faunas and floras between India, Australia, South 

 Africa, and South America seems to be requisite, and even if this were supplied 

 in the most conservative way, it must have seriously interrupted the high-lati- 

 tude circulation of that hemisphere. The constraint of the oceanic circulation 

 in both hemispheres must have greatly reduced the temperature of the polar 

 regions. This quite certainly led to greater differences of temperature between 

 the air columns of different latitudes, and this must have intensified the vertical 

 circulation of the atmosphere, and accelerated the loss of heat from the surface. 



2. Extansion of continental climates. — A second effect of the increase of the 

 land areas was an increase of the continental elements of the climates, and a 

 strengthening of the atmospheric circulation between land and sea. This fur- 

 ther intensified the vertical circulation and accelerated the loss of surface heat. 

 The mountains and other reliefs introduced by the deformation still further 

 aided in checking horizontal circulation and intensifying vertical circulation. 



3. Reduction of humidity. — A third effect was a reduction of the average 

 moisture of the atmosphere. This is not only a firm theoretical deduction from 

 the increase of the land area and the reduction of the water area, but is deposition- 

 ally indicated by the remarkable prevalence of salt and gypsum deposits and 

 of red beds. There is no question that the vapor of water plays a large part 

 in the retention of the heat radiated from the earth, and so acts as a thermal 

 blanket, and hence the reduction of this blanket led to less retention of the solar 

 heat, and hence to a lower temperature. As this was truer of the land areas 

 than of the oceanic, the climate must have been differentiated geographic- 

 ally into intensities of dryness and humidity, and of heat and cold. These 

 must further have involved an increase of convective currents, and hence an 

 additional loss of heat. 



4. Depletion of the heat-absorbing constituents of the atmosphere. — A fourth 

 effect is assigned to a change in the constitution of the atmosphere affecting 

 especially its heat-absorbing constitutents. The reduction of moisture was a 

 part of this change, but reference is here made to the more permanent constituents, 

 particularly carbon dioxide. The increased area of the land, and its increased 

 elevation, gave increased contact between the atmosphere and the rocks of the 

 earth susceptible of carbonation and oxidation, as already indicated. As a 

 result, the atmosphere lost carbon dioxide and oxygen at a more rapid rate 

 than in the previous period. Oxygen plays some part in the thermal blanketing 



