THE POSITION OF THE EARTh's AXIS. Ill 



to put into a definite shape the questions I wish to bring 

 before the notice of any astronomers or physicists who may 

 feel inclined to examine them. 



The cause of the greater warmth in high northern lati- 

 tudes during the Tertiary period has not, according to the 

 opinion of many, yet received any satisfactory solution ; 

 and there seems to be a growing feeling that even if the 

 explanation given by the astronomers of the cause of the 

 cold should be adequate, the explanation of the warmth 

 in previous periods in the arctic regions is much more 

 complicated. 



The flora of the Tertiaries and the indication that they 

 give of the climate of the time have been elaborately 

 worked out by Prof. Heer*, who believes that a gradual 

 diminution of temperature can be traced from the earlier 

 Tertiaries to the later, the Eocene in Central Europe 

 showing a temperature I3°-I4° Cent. (23°-25° F.) warmer 

 than at present, while the Upper Miocene of Oeningen 

 shows only about 7° Cent. (12° F.) warmer. Prof. Heer 

 also thinks that the flora proves that the climate then, as 

 at present, was colder the nearer we approach the pole. 



The flora is the most satisfactory means by which we can 

 draw important conclusions concerning the former tempe- 

 ratures ; but these are all borne out by the faunas. At 

 Oeningen, in Switzerland, a fossil herbarium of wonderful 

 richness, preserved in hard marl, allows us to learn much 

 about the conditions which obtained at the time. The 

 number of species of plants from the quarry is 920, yielding 

 a greater number of species of trees than are now found 

 living in Switzerland. The herbaceous plants are less readily 

 preserved than the leaves of trees ; but as also 844 species 

 of insects have been found fossil, some of which are known 



* ' Flora fossilis Arctica,' i868-i 877, Zurich ; 'Untersuchungen u. d. Klima 

 und Vegetationsverhalt. d. Tortiiirlandes,' Wintherthur, i860; 'Die Urwelt 

 der Schweiz,' 1865. 



