m THE NORTH AND SO UTH. 399 



large island. Hence^ we see that certain plants growing on 

 the more lofty mountains of the tropics in all parts of the 

 world, and on the temperate plains of the north and south, 

 are either the same species or varieties of the same species. 

 It should, however, be observed that these plants are not 

 strictly arctic forms; for, as Mr. H. G. Watson has re- 

 marked, " in receding from polar toward equatorial lati- 

 tudes, the Alpine or mountain flora really become less and 

 less Arctic." Besides these identical and closely allied 

 forms, many species inhabiting the same widely sundered 

 areas, belong to genera not now found in the intermediate 

 tropical lowlands. 



These brief remarks apply to plants alone; but some few 

 analogous facts could be given in regard to terrestrial 

 animals. In marine productions, similar cases likewise 

 occur; as an example, I may quote a statement by the 

 highest authority. Professor Dana, that " it is certainly a 

 wonderful fact that ISTew Zealand should have a closer re- 

 semblance in its Crustacea to Great Britain, its antipode, 

 than to any other part of the world." Sir J. Richardson, 

 also, speaks of the reappearance on the shores of New 

 Zealand, Tasmania, etc., of northern forms of fish. Dr. 

 Hooker informs me that twenty-five species of Algse are 

 common to New Zealand and to Euroj^e, but have not 

 been found in the intermediate tropical seas. 



Prom the foregoing facts, namely, the presence of tem- 

 perate forms on the highlands across the whole of equatorial 

 Africa, and along the Peninsula of India, to Oeylon and 

 the Malay Archipelago, and in a less well-marked manner 

 across the wide expanse of tropical South America, it ap- 

 pears almost certain that at some former period, no doubt 

 during the most severe part of a G-lacial period, the low- 

 lands of these great continents were everywhere tenanted 

 under the equator by a considerable number of temperate 

 forms. At this period the equatorial climate at the level 

 of the sea was probably about the same with that now ex- 

 perienced at the height of from five to six thousand feet 

 under the same latitude, or perhaps even rather cooler. 

 During this, the coldest period, the lowlands under the 

 equator must have been clothed with a mingled tropical 

 and temperate vegetation, like that described by Hooker as 

 growing luxuriantly at the height of from four to five 



