CLIMATIC VARIATIONS — GEEGOEY. 349 



panied by organic solution, from 3 parts to 100 parts in 10,000 — an 

 increase ten times as great as the maximum considered by Arrhe- 

 nius — is inappreciable to man. The ordinary data of mine ventila- 

 tion and the experimental results of Dr. J. S. Haldane and Dr. Lor- 

 raine Smith show that men can stand, without serious inconvenience, 

 an increase of carbonic acid to even 400 parts in the 10,000 ; and as 

 there is no probability of temporary variations to any such degree, a 

 slow increase in the carbonic acid contents of the air would probably 

 have a greater indirect effect upon animals through its action on the 

 temperature than by its direct effect on respiration. 



N oncoincidence of dates. 



The main objection to the atmospheric variation theory is that it 

 does not explain the facts of historical geology. And geologists, as 

 the historians of the earth, test theories whenever possible, by their 

 agreement with contemporary records. 



The influence of variations of the carbonic-acid contents of the 

 atmosphere on temperature should affect the whole world simul- 

 taneously." The change need not be the same in all latitudes, as is 

 shown by Arrhenius's tables; and also by the variation in the pro- 

 portion of cavbonic acid with latitude, which is rendered probable 

 by the evidence adduced by Letts and Blake.'' Nevertheless, it might 

 be expected that corresponding positions in the two hemispheres 

 should be almost equally affected. 



There is, however, no evidence of a glaciation in Europe '^ in 

 Upper Carboniferous or Permian times corresponding to that of 

 South Africfi or Australia, in spite of the unusually extensive knowl- 

 edge of the land conditions of that period. The Indian glaciation 

 of Pokaran in latitude 25° N., and of Chanda in latitude 19° N., may 

 correspond to that of South Africa from latitude 24° S. to 34° S., or 

 of southeastern Australia from latitude 30° S. to 40° S. But the 

 general collapse of the supposed Permian glacial conglomerates of 

 the English Midlands, and the unconvincing evidence collected to 

 support Carboniferous glaciation in France, as by Julien,<^ leaves us 



<^It is sure that accordiiig to tlie results of Muntz and Aubin there is at 

 present a difference in the amounts of carbonic acid in the air of the Northern 

 and Southern liemispheres ; they estimate the mean amount as 0.028 per cent in 

 the Northern and 0.027 per cent in the Southern. This difference follows from 

 the greater area of sea in the Southern Hemisphere, which can hardly have 

 been much greater at any previous period. 



^ E. A. Letts and R. F. Blake, " The carbonic anhydride of the atmosphere," 

 Sci. Proc. Roy. Dublin Soc, Vol. IX, 1900, pp. 179-180. 



c There is some evidence of glacial beds of this period on the east of the 

 Ural Mountains. 



^A. Julien, "Anciens glaciers de la Periode Houlllere dans le Plateau Central 

 de la France," Ann. Club Alpiu Frangais, Vol. XXI, 1894, pp. 28, 



