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



discovered, mostly in the groups of cephalopods, certain pecu- 

 liarities of distribution, consisting chiefly in the presence of 

 certain genera (Phylloceras, Lytoceras, Simoceras) in the 

 southern European deposits, but wanting or represented only 

 rarely in the deposits of the other parts of Europe. The 

 northern boundary of this southern province, the Mediterra- 

 nean, follows, generally speaking, the course of the Alps and 

 Carpathian mountains. In the other parts of Europe, the 

 Jurassic deposits of England, France, Germany, Poland, show 

 further differences from those of Russia ; the former, the Mid- 

 dle-European province, possesses peculiar cephalopod-genera, 

 such as Ojpjpelia, Asjpidoceras, while in the latter, the Russian 

 province, these are nearly wanting and other animals are here 

 abundantly developed, such as species of the group of JBelem- 

 nites excentricus, and of the Lamellibranchiate-genus Aucella. 



Neumayr resolved to investigate the causes of these appar- 

 ent faunistic differences of strata formed at the same times, 

 and his considerations are the following. Such differences 

 may be due either to topographical causes', such as separation 

 of the relative basins by land, or as differences of facies or 

 depth of the sea ; or they may be due to climatic causes. 

 Believing further, to have demonstrated the impossibility of 

 the action of such topographical causes as named, he concludes 

 that the only remaining way for explaining the existing 

 differences is by supposing that climatic differences of the sea 

 are responsible for them. This supposition is strengthened, 

 according to him, by the situation of these " provinces," being 

 limited each to a circumpolar zone around the earth. 



An investigation of Neumayr's views is therefore divided 

 conveniently into three separate parts : 1. An examination, 

 whether differences of the faunas are really present ; 2. An 

 examination, whether the proofs given for the impossibility of 

 the action of topographical causes are sufficient ; 3. An exam- 

 ination, whether the circumpolar zones are confirmed in a sat- 

 isfactory manner. 



But, before this, we have to decide a preliminary question : 

 whether the groups of animals investigated by Neumayr give 

 us a guarantee that their distribution is able at all to indicate 

 climatic differences. Further, in conclusion, we will demon- 

 strate that many additional objections can be made to the 

 climatic zones of the Jura, even if their existence is supposed 

 to be granted. 



I. The group of animals, the fossil remains of which are 

 most especially studied by JSTeumayr, and from the distribution 

 of which his arguments are taken, is that of the Ammonites. 

 This group is extinct in the recent seas ; the now living 



