A. E. Ortmann — Climatic zones in Jurassic times. 265 



ken gegeniiberstehen").* The statement of Niki tin, however 

 (p. 232), that calcareous deposits are almost absent in the 

 Russian Jura, but that where such are exposed corals are 

 found, induces us to accept a causal connection between the 

 two facts. The occurrences of corals is connected with a 

 calcareous development of the facies, and in the Russian Jura, 

 according to the prevailing sandy nature of the deposits, only 

 local formation of Coral-reefs and limestone-deposits was 

 possible. 



The fact that the Aucella-beds are mostly sandy deposits 

 strengthens this supposition so much more, as these beds are 

 wanting in the limestone-facies of Middle-Europe. Thus we 

 are amply justified in looking at the differences in the charac- 

 ter of the facies as the cause producing the faunistic differ- 

 ences of the Middle-European and Russian provinces even in 

 the Ammonite- fauna. 



By these considerations, I think, I have proved that the 

 argument given by Neumayr for the non-existence or non- 

 action of topographical differences upon the distribution of 

 the Jurassic faunas is a complete failure. Only one point 

 may be granted, that a separation by land was not present in 

 an extensive manner. On the other hand we have learned 

 that it is in the highest degree probable, that on the one side 

 differences of depth of the seas, on the other differences of the 

 facies, are the laws governing the faunistic differences. The 

 first cause applies especially to the distinction of the Mediter- 

 ranean and Middle-European provinces, the second to that of 

 the Middle-European and Russian (Boreal) provinces. 



IY. We have still to examine the third point in Neumayr's 

 argument. As a corroboration of the climatic nature of the 

 differences of the Jurassic faunas, he points to the distribution 

 of the different provinces on the earth, which he alleges to be 

 generally parallel to the equator all around the earth, thus 

 forming circumpolar zones. This is the weakest part in Neu- 

 mayr's view, especially because most of the extra European 

 Jurassic deposits are very unsatisfactorily known, and because 

 Keumayr himself was already acquainted with some localities 

 contradicting his theory. 



Neumayr attributes some significance to the supposed fact, 

 that in South Africa and South America Jurassic deposits 

 are said to be present, corresponding in their characters to the 



*In his latest rejoinder to Nitikin (N. J. M. G. P. 1890, 1, p. 142) Neumayr 

 refers to his former paper (1887) as having shown that differences of this kind 

 •were not to be held responsible for the faunistic differences. But he did not 

 even attempt to prove this assertion in that paper. 



