WARM CLIMATE. 127 



may with great probability be regarded as the ancestors of the 



existing species. 



In the Miocene a rich fauna and flora are spread before us, 

 showing the development of a complete series of phenomena of 

 plant and animal life both on land and in the water ; and all 

 agree in telling us that the Miocene country must have had a 

 warm and, indeed, subtropical climate. 



It has been already shown (vol. i. pp. 310, 311) that the flora 

 of the Miocene was much richer in species than that of the 

 present day, and that its numerical proportions are such as now 

 occur in subtropical regions. The insects, reptiles, and Mam- 

 malia also present a surprising abundance of species, such as 

 southern lands alone can now show, and such as is possible only 

 where the earth is clothed by a luxuriant vegetation. That the 

 flora of the Miocene period must have been greatly in excess of 

 the existing Swiss flora is proved by the Swiss Miocene trees 

 and shrubs far exceeding in number of species the united floras 

 of Germany and Switzerland at the present day. The majority 

 of the woody Miocene plants (between two thirds and three 

 fifths of the whole Miocene flora) possessed evergreen foliage, as 

 may be demonstrated by the leathery consistence of the leaves 

 and the analogy of nearly connected living species. This state 

 of vegetation characterizes warm zones (see vol. i. p. 311), 

 and it could not be maintained in a country subject to cold 

 snowy winters such as we now have in Central Europe. A 

 single severe winter would have utterly destroyed evergreen 

 forests similar to those of the Miocene. 



CEningen and the marls of the Schrotzburg have furnished 

 Prof. Heer with remarkable information as to the course of the 

 seasons. Plants, as is well know r n, are dependent on the sea- 

 sons and on climate for the constantly recurring cycle of their 

 development. This influence, however, affects some plants in a 

 greater degree, and other plants in a less degree ; and therefore 

 the intervals of the developmental epochs, such as the period of 

 flowering of the same plants, are not the same in all latitudes. 

 Such epochs in northern latitudes are generally more distant 

 and more distinctly marked, and in the warmer zones they are 

 brought closer together. Whenever we can ascertain what trees 

 burst into leaf and flower in the Tertiary period at the same 



