138 EEV. G. HENSLOW ORIGIN AND DISTllIUUTION 



is signalised in our country by the celebrated Cromer Forest, and 

 the peat or lignite beds on the north coast of Norfolk.*' These are 

 overlaid by a steep cliff of " glacial deposits." The flora of these 

 beds is identical with the existing one ; that is to say, the Scotch 

 tir, accompanied by the Norway spruce (now extinct, but re-intro- 

 duced), both our water-lilies, the buck-bean, alder, etc., then 

 flourished, but with the strange companions of JElephas meridionalis, 

 many Cerin, the Rhinoceros, the great Bos primigenms, the Irish 

 elk, and other extinct animals. 



The reduction of temperature (for the forest-beds indicate as 

 temperate a climate as our own), seen by comparing it with that of 

 the preceding Miocene period, was the antecedent condition to an 

 arctic or glacial state of things shortly to follow, or "the Great Ice 

 Age." The evidence of this, as derived from plants, is seen in the 

 presence of an arctic willow, Salix polaris, found in a deposit over- 

 lying the subtropical Miocene beds at Bovey Tracey. 



Now, as England is at present temperate, and an arctic flora 

 reigns over high latitudes simultaneously with it, so does it seem 

 probable that such was the state of things, if not before, at least 

 soon after the close of the Glacial Epoch ; that when the Cromer 

 Eorest flourished, an arctic flora prevailed simultaneously with it 

 in high latitudes. As, hoAvever, the ice continued to increase south- 

 wards, and the land in all latitudes was encroached upon and ren- 

 dered unfit for such plants to inhabit, they were driven southwards 

 down every meridian, from the arctic regions. The long line of 

 mountains in America, forming an unbroken bridge of transport, 

 enabled many to cross the tropics and so reach the extra-tropical 

 regions of South America. Mr. Belt discovered signs of " glaciation " 

 in Nicaragua down to 2000 feet above the sea, apparently showing 

 that there was a " cooling" going on at least locally in the tropical 

 regions, which would seem to dispose of the difficulty of arctic 

 plants crossing the torrid zone. Similarly in the eastern hemi- 

 sphere, assuming the land to have been continuous, and there 

 are solid reasons for believing it to have been so, the arctic flora 

 would have been able to find a passage from the Himalayas, 

 through eastern China and the Celebes, to Australia, New Zealand, 

 and Tasmania. 



Another suggestion is that the Australian forms came from South 

 America to New Zealand, then Tasmania, and finally Australia ; 

 for the New Zealand flora is strangely like that of South America 

 in some respects, and it has been shown above that Tasmania 

 has more British types than Australia. f 



* Whether the temperate period indicated by these plaut-beds preceded the 

 " Glacial " epoch, or represent interglacial milder periods, is perhaps at present 

 undecided by geologists. 



t Hooker thus sums up bis observations on this dispersion, in his Introductory 

 Essay to the ' Flora of Tasmania,' p. ciii: — "When I take a comprehensive 

 view of the vegetation of the Old World, I am struck with the appearance it 

 presents of there being a current of vegetation (if I may so fancifully express 

 myself) from Scandinavia to Tasmania ; along, in short, the whole extent of that 



