260 Rev. 0. Fisher — On the Formation of Mountains. 



since the crust became rigid on the whole as much as a slag would 

 do in passing from a fused to a devitrified state (a reasonable 

 supposition), this would give a mountain range of something 

 under half a mile high on every hundred miles of surface, 

 calculated in a manner similar to that employed in this paper. 

 If only a part of the area was disturbed, the mountains would 

 be higher.^ And I have now shown how very much less would, 

 in all probability, be the effect produced by the expansions sug- 

 gested by our author. I have not had the good fortune to hear 

 of the " many arguments " which have been urged against this 

 generally accepted theory ; but I think I have seen the solitary one 

 mentioned by Captain Hutton somewhere before — that the earth 

 has been warming instead of cooling since the glacial period. 

 But to this I cannot accede. If we admit that the temperature of 

 the surface as a whole is greater now than it was in a glacial 

 period, it does not follow that the earth is not still cooling. If 

 the surface were kept warmer than the interior, so that in descend- 

 ing the temperature decreased, it would prove it to be on the whole 

 receiving heat, but so long as experiment shows that the interior 

 is hotter than the surface, it must be losing heat^ — not so rapidly 

 certainly, as when the surface was kept more cool, but still losing 

 heat. 



However, it is not probable that on the whole the earth was kept 

 cooler during glacial periods than it is at present. It is more pro- 

 bable that the opposite hemispheres have been affected alternately 

 with such periods,^ and Captain Hutton, at the Antipodes, will do 

 great service if he can elucidate this question. If glacial conditions 

 were universal over the whole globe, it seems that we must look to 

 a change in the condition of the Sun to account for them. 



It may not be out of place to mention shortly the experiments re- 

 ferred to by Babbage and our author, respecting the expansion of 

 stones when heated, and suggest some conclusions from them. 



Lieut. Bartlett's experiments were made under the direction of 

 Col. Totton in 1830, upon blocks of stone 94 inches long ; the varia- 

 tions in length being measured for different temperatures between 

 6° and about 100° F. They appear to have been made under dif- 

 ferent states of atmospheric temperature during rather more than 

 a year. The hygrometric condition of the stones was not taken 

 account of. There were discrepancies observed in the rates of expan- 

 sion in different experiments, and " it is probable that many of the 

 discrepancies noticed were owing to the hygrometric ^ states of the 

 stones," which were " not recorded." 



Mr. Adie's experiments were made with great care upon rods of 

 stone 23 inches long, of different kinds, both when moist and dry. 



1 Cam. Phil. Trans., loc. cit. ; and Geol. Mag., Vol. YII. p. 68. 



2 See Maxwell's Theory of Heat, p. '247. 



3 See a paper on "The Physical Geography of the M edeterranean during the 

 Pleistocene Age," by W. Boyd Dawkins, M.A., F.E.S., in the "Popular Science 

 Ecvicw," for April, 1873, p. 159. 



* American Journal of Science, vol. xxii., p. 138. 



