CLIMATES. 205 



does not afford any evidence of changes of climate, and that the 

 climate of the Arctic zone, at least during the Carboniferous and 

 Lower Cretaceous periods, did not differ from that prevailing in 

 the latitudes of Switzerland. In the Tertiary epoch a distribu- 

 tion of heat is observable in zones ; but the decrease of tempera- 

 ture towards the poles was much less marked than at present. 

 Whilst the tropical zone was probably scarcely warmer than in 

 our time, Central Europe, during the Lower Miocene period, 

 had a climate nearly equivalent to that of the southern United 

 States (p. 140) and to the climate of the north of Africa. Un- 

 der the Arctic zone in 78 N. lat., the island of Spitzbergen was 

 covered with forests of swamp-cypress (Taxodium distichum), 

 Sequoia, numerous species of pines, plane-trees, walnuts, oaks, 

 and lime-trees a fact which justifies the belief that forest vege- 

 tation extended to the pole itself, if this central locality was 

 surrounded by solid ground. The difference between the fauna 

 and flora of the Miocene epoch and that of the present day 

 must have increased in passing from the equator towards the 

 poles. 



A decrease of temperature took place during the Miocene 

 period (pp. 137, 138) ; and the diminution of heat continued 

 during the Pliocene epoch, as appears incontestably from the 

 change brought about in the marine fauna (p. 172). At the 

 close of the Pliocene epoch the temperature may have been 

 similar to that of the present day. During the drift-period it 

 sank several degrees below the present mean temperature, and 

 remained at this low point for thousands of years, thus consti- 

 tuting the first Glacial period. The formation of the Lignites, 

 which followed this period, indicates a reelevation of temperature 

 in Switzerland; and thus the temperature reached the point at 

 which it now stands. In the south of France and in England 

 the temperature seems to have been a little higher; in the 

 forest-bed of the Norfolk coast the same species of plants have 

 been found as in the Swiss lignite-beds, as well as the same 

 species of rhinoceros (R. etruscus) and the same elephant (E. 

 antiquus) ; to these animals must be added Elephas meridionalis 

 and Hippopotamus. Together with these Pachyderms, there 

 have been discovered at Grays Thurrock, in the county of Essex, 

 a bivalve shell (Cyrena fluminalis) which no longer exists in 



