Searles V, Wood, Jun. — The Climate Controversy, 391 



to establish, viz. that the refrigeration of the northern hemisphere 

 which would arise from the occurrence of the aphelion in its winter, 

 would push the equatorial belt of calms some degrees of latitude further 

 south, and with it the north-east trade, to which he insists the Gulf- 

 stream is due. In reference to this oscillation of the equatorial belt of 

 warmth, Mr. Croll quotes the adoption by Mr. Darwin of the Excen- 

 tricity theory as accounting for the diffusion of certain species of 

 plants, which occur alike in the temperate, but not in the tropical 

 regions of both the northern and southern hemisjpheres. The view 

 is, that as the cold of the northern hemisphere became greater, 

 some of the more dominant and wide-spreading northern temperate 

 forms invaded the equatorial lowlands, and as the two hemispheres 

 gradually recovered their former temperature, that then, although 

 most of these northern temperate forms so living in equatorial 

 lowlands would have been driven to their former homes or destroyed, 

 some of them would have ascended any adjoining highland, where 

 they would have survived like the Arctic forms on the mountains of 

 Europe. Then, as the southern hemisphere was in turn subjected 

 to a severe glacial period with the northern hemisphere rendered 

 warmer, the southern temperate forms would invade the equatorial 

 lowlands to intermingle with the northern forms so left on the 

 mountains, but from which they now descended. As the warmth 

 again increased, these southerners would return to their former 

 homes, leaving some species on the mountains, and carrying south- 

 ward with them some of the northern temperate forms which had 

 descended from their mountain fastnesses. 



The necessity for this complex explanation is not apparent, at 

 any rate so far as the continent of America is concerned ; as all 

 that would seem necessary for the passage of temperate forms of 

 plants from north to south, and mce versa, is a line of mountains 

 running in that direction of elevation sufficient to induce on their 

 flanks or summits temperate climates in tropical latitudes ; and this, 

 if we make allowance for the proportionate refrigerence of all lati- 

 tudes during the glacial period, we find on the American continent ; 

 since those parts of the chain which now, in Central America, do not 

 from their small altitude furnish this condition of things, would have 

 had at that time temperate climates on their flanks or summits, and 

 the intervals of hot lowland have been so reduced as not to prevent 

 the occasional migration of temperate climate plants from one hemi- 

 sphere to the other. On the other hand, the common origin of the 

 Greenland blubber whale (Balana mysticetiis), and the right whale 

 of the Antarctic (Balcena australis) at a late period, which has been 

 generally admitted is repugnant to that oscillation of the equatorial 

 warm water belt without curtailment of its breadth, which forms 

 part of the Excentricity theory ; and seems to indicate that a 

 curtailment of the breadth of this belt, which now forms so 

 impassable a barrier between these allied species, did actually 

 take place by means of that simultaneous refrigeration of both 

 hemispheres which all the facts hitherto observed in reference 

 to the Glacial period proper appear to me to prove. 



