WARM ZONE. 133 



We now come to the autumn, when the planes and liquid- 

 ambars were hung with their spherical fruit- catkins, some of 

 which probably, as in their existing relatives, remained on the 

 trees until the following spring, and were buried in a soft marl 

 at the same time with the flowers and other vernal organs. 

 Most of the trees with deciduous leaves bore their foliage longer 

 than those now growing in Switzerland ; so that the forests, so 

 far as they consisted of such trees, probably did not lose their 

 leaves until quite the end of the year. 



Whilst these trees had definite periods of repose in the course 

 of their life, others retained their leafy covering throughout the 

 winter ; many of them probably put forth flowers and fruit all 

 the year round; so that in this primaeval forest life was constantly 

 renewed in wonderful abundance, reminding us of those fortu- 

 nate zones where nature never goes to rest. 



If we bring together those species of the Miocene flora which 

 can be compared with living species, we find those of the tempe- 

 rate zone* represented by 131 species, those of the warm zone 

 by 266 species, and those of the torrid zone by 85. The majority, 

 therefore, indicate the warm zone, comprising regions which 

 have an average annual temperature of between 59 and 77 

 Fahr. (15 and 25 Centigrade), and are situated between 45 and 

 24 N. lat. This is a broad zone; but a careful comparison of 

 the most important forms of plants does not allow us to reduce 

 it within more restricted limits. 



* To the tropics (or torrid zone) Prof. Heer refers the countries lying be- 

 tween the tropics; to the warm zones the southern part of the United States 

 of America, the mountain-country of Mexico, the Mediterranean countries, 

 Asia Minor, Southern Caucasus, Persia, Northern India, Japan, Chili, the 

 Cape of Good Hope, and extra-tropical Australia ; and to the temperate zone 

 those countries in the northern hemisphere which lie between 45 and 58 N. 

 lat. In America Prof. Heer reckons Virginia and Kentucky among the 

 northern States. According to Asa Gray, the boundary-line thus drawn 

 separates naturally the warm southern States from the colder northern ones. 

 "With regard to the numbers given in 1he text, it is to be observed 1hat 

 they are not obtained by the addition of the numbers given in vol. i. p. 370. 

 Such an addition would not have led to a correct result, as the same species 

 appears under several categories whenever its living analogue occurs in diffe-> 

 rent parts of the world or in different zones. 



