Refrigeration of the Earth. 219 



by the escape of heat, there remains only one other mode of 

 explaining it, — a continually diminishing supply. The latter 

 k the explanation offered by Mr Lubbock. Sir John Herschel 

 also has brought into view causes within the range of physical 

 astronomy, which, independently of a loss of internal heat, pro- 

 duce a slow but certain diminution of temperature on the sur- 

 face of our globe*. These auxiliaries, however, are insufficient. 

 Mr Lyell has offered another solution of the problem, depend- 

 ing not on celestial but terrestrial causes. The chapter that 

 contains it abounds in valuable information and ingenious reason- 

 ing ; but when the author tells us that f in every country '* the 

 land has been in some parts raised, in others depressed, hy which, 

 and other ceaseless changes, the corifiguration of the earth'' s sur^ 

 face has been remodelled again and again since it zvas the hahi" 

 tation of organic beings, and the bed of the oceaii lifted up to 

 the height of the highest mountains^"* I cannot but wish that 

 he had stated this as an opinion, not as a fact. 



All these theories have one defect in common ; they do not 

 meet the whole of the case. We have to explain not only the 

 cooling gradual during the long interval that occurred between 

 the formation of the carboniferous beds and the chalk, but also 

 the sudden chill which followed, and seems to have continued 

 from that time to this. There is yet another element to be 

 taken into account. The coal-beds of Melville Island contain 

 various plants, natives of the country where they are found, and 

 which, if we may trust analogy, require for their healthy growth, 

 or for their growth at all, not only tropical heat |, but a tropi- 

 cal apportionment of the periods of exertion and repose. It is 

 a botanical impossibility that such plants could have flourished 

 in a region in which they must have been stimulated by months 



• The Baobab tree of Senegal is supposed by Adanson to have attained 

 the age of 5150 years, and De CandoUe attributes to the Cupressus disiicha of 

 Mexico a still greater longevity. (Lyell, vol. iii. p. 99.) 



If these opinions be correct, it seems improbable that any great change 

 either of level or climate can have taken place at these spots within the last 

 5000 years. 



f Principles of Geology, vol. i. p. 113. 



$ Since this passage was written,doubts have been expressed whether the 

 specimens of these plants preserved at the British Museum are suflSciently 

 distinct to warrant the inference. 



