20 EARLY MAN IN BRITAIN. [CHAP. n. 



Britain connected with North America. 



From the coast-line above mentioned the land ex- 

 tended northwards and westwards, far away from our 

 present shores, and is proved by the examination of 

 the forests and of the animals to have been continuous 

 with the North American continent. The chief botanists 1 

 of the present time Hooker, Dyer, Saporta, Dawson, 

 and Asa Gray are agreed that the north polar region 

 was the centre from which the Tertiary floras have been 

 dispersed over the new and old worlds. According to 

 Saporta, the marked difference between summer and 

 winter in the polar regions has first left its impress in 

 the dicotyledons with deciduous leaves, which were 

 unknown on the earth before the Cretaceous age. Their 

 introduction was the greatest revolution in the vegetable 

 kingdom, as yet observed, and when once evolved they 

 increased rapidly in numbers and diversity of forms. As 

 the polar temperature was lowered, the trees of warm 

 habit were pushed farther and farther south, away from 

 their original birthplace, and ultimately only survived in 

 isolated districts, now separated from each other by great 

 tracts of sea, or great areas of desert or of mountain. 

 In consequence of this there is an almost unbroken 

 sequence to be observed in the floras succeeding each 

 other in the northern hemisphere, from the Eocene age 

 down to the present day. " There is no great break/' as 

 Mr. Starkie Gardner observes, " in passing from one to 

 the other, when we compare them over many latitudes, 

 a nd but little change beyond that brought about by altered 



1 Hooker, Proceed. Royal Soc. xxviii. p. 51. Saporta, Les Anciens Cli- 

 mats de I' Europe et le Developpement de la Vtfge'tation. Association Franchise, 

 Havre, 1877. Dawson, Princetown Rev. 1879, p. 182. 



