380 Correspondence — Mr. T. Mellard Reade. 



He does not, however, allude to, and therefore possibly has never 

 taken the trouble to read, the several direct n^plies I have given to 

 this very objection when made by people who had failed completely 

 to understand what my theory', as originally published in 1886, 

 really is. One such complete refutation is contained in a paper 

 in this Magazine in May, 1894:, entitled, " On the Result of 

 TJnsymmetrical Cooling and Redistribution of Temperature in a 

 Shrinking Globe as applied to the Origin of Mountain Ranges," in 

 which I have dealt broadly with the whole subject, and have shown, 

 that the effect of sedimentation is to cbeok the Earth's cooling in 

 the area in which the sediments are being laid down. The form 

 in which the case is stated, both by Le Conte and Davison, shows 

 an entire misapprehension of the whole problem. It is not that the 

 sediments abstract heat from the portion of the Earth's crust upon 

 which they lie or with which they are in contact, but that they 

 simply prevent the outflow and consequent loss of that heat from 

 the nucleus which would otherwise be dissipated into space, and 

 this heat thus retained expands them. I have shown in the paper 

 referred to that it is to the redistribution of heat in the crust, and 

 the consequent alteration of stresses and strains, that we are to look 

 for the effective cause of mountain folding and upheaval. To say, 

 therefoi'e, that the "-increased heat must he taken from someioTiere else " 

 is an obvious truism which conceals the implied fallacy that sedi- 

 mentation at a certain point will cause a greater loss of heat at that 

 point than at the surrounding points whereon no sedimentation has 

 taken place, and this is not true — it is exactly the reverse — less 

 heat will be lost at that point. 



Mr. Davison, thinking to strengthen his objections to the expansion 

 theory, now quotes Herschel and Lebour to show that wet rock is 

 a better conductor than dry rock. This was well known to me, 

 through their admirable researches, before I penned a line of the 

 " Origin of Mountain Ranges." Doubtless superficial layers of wet 

 sediment may be better conductors of heat than the average earth- 

 crust, but consolidated sediments miles thick are not likely to be 

 in the moist condition common to surface-rocks. Herschel and 

 Lebour's investigation, so far from supporting Mr. Davison's con- 

 tentions, are on the whole distinctly in favour of my views. Indeed, 

 I cannot do better than reproduce here some of their extremely 

 acute observations on the results of their experiments, which have 

 so far not received from geologists and physicists the attention they 

 deserve — "In the first place, it seems to be proved by our experi- 

 ments that the conducting-power of different rocks varies strictly 

 according to their lithological character. Very crystalline rocks, 

 such as granite and serpentine and statuary marble, allowed heat to 

 pass rapidly through them ; slate-plates, with their uncrystalline 

 compact structure, had a still higher degree of conductivity. The 

 crystalline nature of a rock alone is not, therefore, the lithological 

 test of its conductivity. The lowest powers of conductivity were 

 found to belong, among the specimens experimented on, to shale ; 

 the black shale, which was lower than the grey, is softer and more 



