202 Report of the State Geologist. 



south and east of France. The coral horizons of the Upper Juras- 

 sic are now distributed in five zones, which present all these 

 three facies ; these zones characterize the Rauracian, Astartian, 

 Pfcerocerian, Yirgulian and Portlandian deposits. 



The same phenomena present themselves later in other local- 

 ities. The Neocomian and the Gault have a corallio facies called 

 TJrgonian ; the Turonian is represented in the south by the facies 

 with Hippurites, for which also a distinct horizon has been named. 

 Finally, if we turn our attention to the more ancient deposits, 

 we see that the corallio horizons, formerly referred to the Devon- 

 ian and Carboniferous as especial zones, have been recognized as 

 the equivalents of the schistose formations which surround them. 



§ 4. Infltjenoe of Climate. 



Effect of temperature. — Temperature exercises a considerable 

 influence on the distribution of animals ; the factor which at the 

 present epoch seems the most important in this regard is the 

 maximum of cold attained during the winter.* We have, there- 

 fore, drawn on the terrestrial maps lines called Isocrymal^ which 

 mark the mean temperature of the coldest 80 days of the year. 

 The distribution of anitnals is in direct relation to the lines so 

 determined, which notably diverge from the geographic paral- 

 lels. In this way principal zones are established, which can be 

 enumerated for each hemisphere ; the arctic, the boreal, the cold 

 temperate, the warm temperate and the tropical zone. The limits 

 of these zones are more clearly indicated than would at first 

 sight be believed. 



Effect of natural barriers. — It is a known fact that the lati- 

 tude is not the only factor which determines the climate 

 of a region. Every one is aware that the climate is much more 

 uniform and temperate on the sea coast than in the interior of 

 the great continents. But in regard to the sea itself, the mean 

 temperature may vary considerably in places quite near each 

 other, consequent upon the presence or absence of a barrier 

 furthering or impeding communications with colder or warmer 

 waters. This is the reason why at present the Ked Sea and the 

 Mediterranean have very differing temperature, notwithstanding 

 their proximity. The presence of barriers of solid ground, either 



♦ This factor Is more Important from the biologic point of view than the mean temperature of the 

 entire winter which determines the Isochimenal lines . 



