376 NATURAL SCIENCE. Nov., 



But, say my critics, your theory does not give lateral movement 

 sufficient, we want much more ; to which I have replied and sustained 

 the affirmation by figures, that it gives more lateral movement than 

 any of the other contending theories. I have also shown, and this 

 view has been endorsed by no less an authority than Stefani, 2 that the 

 amount of lateral movement required for mountain building is very 

 much less than what is given by measuring the folds of mountain 

 ranges and comparing their length with the base line of the chain. 

 The assumption that the difference represents the amount of move- 

 ment that has taken place is fallacious, because the reproduced arches 

 never existed, and the strata have been lengthened by rolling out. 



The subject of mountain building is so intricate and complex, 

 and has so many aspects, that it would take much more space than is 

 at my disposal to do justice to it ; but before concluding these 

 observations it will be necessary for me to reply to the objection con- 

 sidered by Le Conte to be fatal to my theory. He says, " But the 

 fatal objection is that brought forward by Davison. It is this : 

 sedimentation cannot, of course, increase the sum of heat in the earth. 

 Therefore the increased heat of the sediments, by rise ofisogeotherms, 

 must be taken from somewhere else. Is it taken from below ? Then 

 the radius below must contract as much as the sediments expand, and 

 therefore there will be no elevation. Is it taken from the containing 

 sides ? Then the sides must lose as much as the sediments gain, and 

 therefore must contract and make room for the lateral expansion, and 

 therefore there would be no folding and no elevation. I do not see 

 any escape from this objection." 



This, in my view, is a formal objection, and formal only. The 

 criticism is underlaid by the profound misconception that the sedi- 

 ments abstract heat from the earth. So far from this being the case, 

 they conserve it and retain heat that would otherwise be wasted tnto space. 

 They act as a blanket or top-coat would do to the human body, as 

 pointed out by Herschell and Babbage. The radial contraction of 

 the earth is less under the blanketing sediments than under the other 

 portions of the crust. Looked at in even this partial manner, there is 

 practically no difference between a radial expansion of a part of the 

 globe under the sediments — the only expansion apparently contem- 

 plated by Le Conte as effective — and a radial contraction of the 

 surrounding crust of the earth. It is a question of relative movement 

 and of differential ', not absolute, heating. Increase of the sum of heat in 

 the earth is entirely beside the mark. The answer is therefore simple 

 and conclusive. The sediments neither abstract heat from below nor 

 from the sides, they conserve and utilise what would otherwise be 

 wasted. The flow of heat from below could not be quickened by the 

 laying down of sediments, unless they were at a lower temperature 

 than the surface of the earth's crust on which they were deposited. 



2 "Le Pieghe delle Alpi Apuane," p. no, Firenze, 1889. 



