A. E. Ortmann — Climatic zones in Jurassic times. 269 



tion. Such a current is according to his map hardly possible. 

 The course in the direction first mentioned is impossible, 

 because no conditions in the configuration of land and sea were 

 present there which could effect a current in this direction 

 (like the Kuro-Siwo and Florida current of recent time). The 

 alleged curve of the current at its most northern point would 

 be also astonishing : why does this current not carry its warm 

 water farther northward into the Russian province? If it 

 went in the opposite direction, we must ask : where did it 

 come from, and what was the cause producing such an abnormal 

 movement of water in a direction never displayed by any 

 important current of the recent seas? And a current effecting 

 such striking and sharp differences of temperatures must neces- 

 sarily have been an important one ! ' 



I think, however, there is no profit in trying to construct 

 the ocean currents of Jurassic age. But if we adopt the con- 

 figuration of land and sea given in Neumayr's map, there can 

 be no doubt, I believe, that only one kind of movement of the 

 surface water of the sea was possible in all these parts under 

 discussion, namely a general current running from East or 

 North-East to the West or South-West. Then from the 

 Russian basin a cool current would run into the Middle- 

 European and Mediterranian provinces, and the course of the 

 northern limits of these two provinces should be very different 

 from that given by Neumayr. These limits could not show a 

 convexity toward the North just opposite the main opening, 

 through which the cool water was discharged, but we should 

 expect a southward curve of these lines. 



Under such conditions of things, since it is at present utterly 

 impossible to get an approximate idea of the Jurassic currents, 

 it would be profitable to have recourse to such theories only in 

 the most desperate cases, where no other explanation is possible. 



The results obtained by these considerations may be summed 

 up as follows. The differences observed in the faunas of the 

 Jurassic deposits are not caused by climatic differences. The 

 arguments of ISTeumayr for the non-action of the topographical 

 conditions are partly incomplete, partly they fail to convince. 

 On the contrary, I have shown, that even conditions of the 

 latter kind, differences of depth of the seas and differences of 

 the facies play the chief part in influencing the distribution of 

 the Jurassic fauna, and that the existence of climatic zones in 

 the Jurassic seas is not only not proved, but extremely improb- 

 able. Therefore it would be well to abandon entirely Neu- 

 mayr's theory of climatic zones in Jurassic time,* and it would 



* In order to prevent any misunderstanding, I wish to say expressly, that I 

 do not deny the existence of changes in temperature and differences in climate in 



