A. E. Ortmann — Climatic zones in Jurassic times. 267 



The tracing of the different Jurassic zones around the other 

 parts of the earth, especially across the American continent, is 

 so problematic, that it is not worth while to go more into 

 details here.* 



The instances, however, given above are wholly sufficient to 

 conclude, that a circumpolar arrangement of the different 

 Jurassic faunas is not yet proved ; on the contraiw, that some 

 facts are known wholly dangerous to that theory. 



V. But even in the case, that it may be granted, that it is 

 neither proved nor refuted, whether the differences of the 

 Jurassic faunas are due to topographical or to climatic causes, 

 and even if we suppose that the action of the latter may have 

 been possible, we will find that such a supposition meets 

 difficulties hard to solve. 



1. As we have seen above, Nikitin recognized the presence 

 of Reef- corals in the Russian Jura, that is to say, in Neumayr's 

 Boreal zone. Neumayr indeed denies the value of the Reef- 

 corals as evidence for forming an opinion as regards the tem- 

 perature of the sea water, but as I pointed out above, the 

 Reef-corals are the only group of animals allowing a some- 

 what sure conclusion as to the former climatic conditions, and 

 I can not strongly enough emphasize that I differ in this 

 respect entirely from Neumayr. Therefore, I am convinced, 

 that the presence of Reef-corals indicates a warm, and espe- 

 cially an equally warm temperature of the seas inhabited, such 

 as now prevails in the tropical seas. If such a temperature 

 was present in the boreal Russian basin, we have to ask : what 

 kind of temperature-conditions prevailed in the temperate and 

 equatorial zones of the Jurassic time? Then we would be 

 induced to believe, that the equatorial seas of the Jura pos- 

 sessed a degree of heat which, compared with the recent con- 

 ditions, would not have permitted at all the existence of animal 

 life! 



2. If we compare the temperature zones of the recent seas f 

 with the supposed temperature zones of Jurassic age as con- 

 structed by JSTeumayr (1890, p. 336), we shall find that the 

 latter are nearly the same as the former, at least as regards 

 their distance from the equator. Even in some cases in 

 Neumayr's map such places belong to a cooler zone, which are 

 nowadays warmer. For instance, New Zealand and Port 

 Elizabeth are situated in his map distinctly in the temperate 



* The occurrence of Aucella-beds like the Russian is indicated by Nikitin 

 (Neues Jahrb. Min. Geol. Pal. 1890, II. p. 273) in tropical America, near St. Luis 

 Potosi, Mexico. If this fact should be confirmed, it would prove an additional 

 argument against Neumayr's theory. 



f See the map accompanying my book : G-rundziige der marinen Tiergeographie. 



Am. Jour. Sci. — Fourth Series, Vol. I, No. 4. — April, 1896. 

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