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



zone, while they lie now, if not within the tropical zone, at 

 least on the border of it. An arctic zone can be distinguished 

 in the present seas only witli difficulty from the temperate 

 zone : Neumayr's boreal zone extends so far southward, that it 

 is hard to believe that it existed at all.' 



According to our knowledge of the climatic conditions of 

 former times, especially of the Tertiary age, there was a grad- 

 ual decreasing of the temperature of the earth, beginning at 

 the poles, and we are accustomed to believe that the climatic 

 conditions now prevailing form the most extreme degree of 

 cooling ever present on the earth. Then it would be in] possi- 

 ble, that at any time in the past a climate existed which, was 

 cooler or was more differentiated than the present climate.* 

 Especially, we can not make such a supposition for the Juras- 

 sic age, passed by long ago, and the climatic conditions of 

 JSTeumayr's map agreeing with the recent ones are utterly 

 impossible. This striking improbability is the more conspic- 

 uous as we compare the supposed Jurassic climate of Neumayr 

 with that of the older Tertiary times, as I have already done 

 elsewhere, f 



In the passage just referred to I remarked, that Neumayr 

 perhaps intended to express no judgment of the actual temper- 

 atures at Jurassic times, but that he had in mind only that a 

 difference in temperature was present. But then we would be 

 induced to accept for his boreal zone a climate like that of the 

 recent tropics, and we would be confronted with the same 

 difficulty as discussed under No. 1. 



3. Remembering the climatic conditions of the recent times 

 we find, that climatic limits generally are not very sharp, but 

 that there are zones of transition interposed. The limits of 

 Neumayr's Mediterranean and Middle-European provinces are 

 very sharp, so that we can not expect that there prevailed 

 normal conditions. Neumayr himself is aware that these 

 limits are unusually sharp ones, and he explains this fact by 

 supposing that there was a current of warm water present. 

 This supposition, however, is a pure imagination, supported 

 absolutely by nothing. 



4. But we will examine this current- theory more closely. 

 Neumayr says (1871, p. 525), that this current coming from 

 the South- West reached in the neighborhood of Cracow its 

 most northern point, and curved then in a south-easterly direc- 

 tion — or the course of this current was in the opposite direc- 



* Perhaps one would refer to the conditions of the "ice age" as representing 

 the most extreme cooling: but I remark explicitly, that I regard the so called 

 "ice age " as a local feature of the subrecent time, which is not at all related to 

 the general cooling of the earth. 



f Grundzuge der marinen Tiergeographie, 1896, p. 62, 63. 



