SCIENCE-GOSSIP. 



warmer parts of England. The only other sug- 

 gestion is a post-glacial land connection between 

 Ireland and the North of Spain, for which there 

 appears to be no independent evidence. It remains, 

 then, to examine the possibility that they may have 

 remained there during glaciation. Suppose that 

 during the warm period which preceded glaciation, 

 the above species were widely spread over Britain 

 and Ireland. Then, as the cold increased and 

 glaciation came on, they would be driven south, 

 and the spot where they would be most likely to 

 survive would be the south-west corner of Ireland, 

 provided our shores were washed, as they are 

 to-day, by the Gulf Stream during the Glacial 

 period. There is evidence that such was the case, 

 because: (a) palaeontology indicates that a warmer 

 climate prevailed on the western shores of Britain 

 than on the eastern ; (b) glaciation extended 

 further south in North America than in Western 

 Europe, as it does to-day. Prof. Forbes (" Fauna 

 and Flora of the British Islands ") has expressed 

 the opinion that this peculiar flora migrated 

 to Ireland before the Glacial period. If this is 

 the true explanation, then we see the possi- 

 bility that a considerable portion of our vegeta- 

 tion may have survived glaciation. There remains, 

 however, the possibility that the flora of the south- 

 west of Ireland may have reached its present station 

 by aid of bird migration in post-glacial times. 



Another botanical fact which has been generally 

 explained as the result of the Glacial epoch, is the 

 similarity and close relationship to northern forms 

 of the plants inhabiting the higher, and conse- 

 quently colder, regions round the equator. Thus, 

 Thomson, the African traveller, in describing his 

 ascent of Kilimanjaro, writes : " The occurrence of 

 brambles, brackens, male and lady ferns, various 

 spleenworts, maidenhair, and mountain polypody, 

 would have made us imagine we were in Europe, 

 but for the unusual profusion and rank luxuri- 

 ance "(■»). Mr. Wallace, in describing the flora of 

 Mount Pangerango,inJava,-writes: "At about 8,000 

 feet European forms of plants become abundant. 

 Several species of honeysuckle, St. John's wort 



.and guelder rose abound A few of 



the smaller plants (Plantago major and P. lanceolata, 

 Sonchus okraceus and Artemesia vulgaris) are identical 

 with European species " ( 5 ). A somewhat similar 

 state of things occurs all round the equator. These 

 temperate forms are supposed to have been driven 

 towards the equator by the glaciation of the 

 northern part of the hemisphere in which they 

 originated. When temperate conditions returned, 

 they are supposed to have ascended the mountains 

 in search of a temperate climate. The remarkable 

 resemblance between certain plants in far distant 

 temperate regions, and on opposite sides of the 



(*) " Through Masai Land," p. 144. 

 I 5 ) " Malay Archipelago," pp. 182-185. 



equator, receives its explanation as the result of 

 glaciation. 



While the former can be explained as the result 

 of glaciation on any theory, the latter is supposed 

 to bear special witness to the truth of the astro- 

 nomical theory. Thus, Sir Robert Ball claims the 

 distribution of these plants as evidence of the truth 

 of the theory of glaciation set forth in " The Cause 

 of an Ice Age." The way in which the astro- 

 nomically-produced glaciation enabled the plants 

 to cross the equator is as follows : certain plants 

 are natives of temperate regions in the northern 

 hemisphere, and this hemisphere begins to undergo 

 glaciation. These plants will be driven south- 

 wards by the cold. It is assumed that they will 

 be driven as far south as equatorial regions. When 

 the northern hemisphere becomes warmer again 

 the plants will be forced to seek a more congenial 

 climate by ascending equatorial mountains. This 

 accounts for the band of temperate plants on the 

 highlands round the equator. According to the 

 astronomical theory, as the northern hemisphere 

 grew warmer the southern grew colder, and finally 

 became glaciated. It is assumed that the tempe- 

 rate flora of the mountains would then be able 

 to descend to the equatorial plains south of the 

 equator. They would remain in equatorial regions 

 as long as glacial conditions continued in the south- 

 ern hemisphere, but as these passed away the 

 increasing warmth would drive them south until 

 they reached southern latitudes as high as those 

 northern ones from which they started. 



The objection to this explanation is that it is 

 only the temperature of one season of the tropical 

 year which is reduced during glaciation on the 

 astronomical theory ; the other season becomes 

 hotter. According to Sir R. Ball's data, the 

 average winter temperature would be reduced 

 21 F., and this would give one season of the 

 tropical year with a temperature perhaps equal to 

 our summer. But as the temperature of the other 

 season would be increased 42 , the tropics would 

 be even less fit for the maintenance of temperate 

 plant-life than they are to-day. In fact, it may 

 be said without reserve that the maintenance of 

 Arctic plant-life on the astronomical theory on the 

 area between temperate regions, and equatorial 

 mountains during the long period of glaciation 

 would be impossible. Mr. Clement Reid has 

 concluded from geological evidence that during 

 glaciation the temperature increased rapidly 

 towards the south. Thus, while glacial Britain 

 was 20 colder than it is to-day, the shores of the 

 Mediterranean were only 5 below their present 

 temperature. At this rate of progression, we can 

 scarcely suppose equatorial lands would be any 

 cooler at all. 



Failing glaciation, however, bird migration may 

 be suggested as at least a partial explanation of 



