CLIMATES. 263 



gard to all the older geological periods from the Carboniferous 

 to the Tertiary, their plants and animals, so far as they can be 

 compared with those now living, approach nearest to those of 

 warm and torrid zones \ and Prof. Heer cannot conclude with 

 any certainty as to there having been any rising or falling 

 of the temperature during this immensely long time. In the 

 Tertiary period, and especially during the Miocene epoch, 

 abundant materials illustrative of temperature are found; and 

 Prof. Heer has therefore entered into detail on this subject 

 (p. 126 &c.). He has found that, in the time of the Lower 

 Miocene, the climate of Europe was about 9 C. (or 16'2 P.) 

 warmer than at present, and in that of the Upper Miocene the 

 European climate was about 7 C (or 12'6 P.) warmer than in 

 our time, and that even then a distribution occurred of heat in 

 zones, of which no traces are found in the most ancient periods. 

 This higher temperature of Swiss Miocene land may be in part 

 explained by the form of Europe at that time. A different dis- 

 tribution of land and water is seen in the map of Central Europe 

 (fig. 154, vol. i. p. 296) at the Middle Miocene period. The 

 eastern sea, which extended into S witzerlaiid, must have exerted 

 a warming influence, as it was connected with the Indian Ocean 

 through the Red Sea, and perhaps also through the Persian 

 Gulf. From this tropical sea a current of warm water, like the 

 existing Gulf-stream in the Atlantic Ocean, must have flowed 

 towards the northern seas and warmed their waters, exerting a 

 powerful influence upon the conditions of temperature of the 

 surrounding lands by means of the broad arms of the sea which 

 penetrated into the heart of Europe. The winter temperature 

 must have been elevated, and the climate must have been more 

 insular and uniform. The sea surrounding the land must have 

 produced a moist climate ; and the mountains, which, although 

 low, were nevertheless in existence, must have contributed to 

 the condensation of vapours lising from the sea, and to their 

 conversion into rain. The Gulf-stream, after being warmed in 

 Central America, moves across the Atlantic to Western Europe, 

 and raises the mean annual temperature of Western France (in 

 the latitude of Rochelle) by about 4 C. (or 7'2 P.). If a 

 similar influence be assumed for Central Europe from the Mio- 

 cene Indian Gulf-stream, we obtain the same elevation of 4 C., 



