132 GEOLOGY [Chap. IX 



Letter 487 To C. H. L. Woodd. 



Down, March 4th [1850]. 

 I have read over your paper 1 with attention ; but first let 

 me thank you for your very kind expressions towards myself. 

 I really feel hardly competent to discuss the questions raised 

 by your paper ; I feel the want of mathematical mechanics. 

 All such problems strike me as awfully complicated ; we do 

 not even know what effect great pressure has on retarding 

 liquefaction by heat, nor, I apprehend, on expansion. The 

 chief objection which strikes me is a doubt whether a mass 

 of strata, when heated, and therefore in some slight degree at 

 least softened, would bow outwards like a bar of metal. Con- 

 sider of how many subordinate layers each great mass would 

 be composed, and the mineralogical changes in any length 

 of any one stratum : I should have thought that the strata 

 would in every case have crumpled up, and we know how 

 commonly in metamorphic strata, which have undergone heat, 

 the subordinate layers are wavy and sinuous, which has always 

 been attributed to their expansion whilst heated. 



Before rocks are dried and quarried, manifold facts show 

 how extremely flexible they are even when not at all heated. 

 Without the bowing out and subsequent filling in of the roof 

 of the cavity, if I understand you, there would be no sub- 

 sidence. Of course the crumpling up of the strata would 

 thicken them, and I see with you that this might compress 

 the underlying fluidified rock, which in its turn might escape 

 by a volcano or raise a weaker part of the earth's crust ; but 

 I am too ignorant to have any opinion whether force would 

 be easily propagated through a viscid mass like molten rock ; 

 or whether such viscid mass would not act in some degree 

 like sand and refuse to transmit pressure, as in the old 

 experiment of trying to burst a piece of paper tied over the 

 end of a tube with a stick, an inch or two of sand being only 

 interposed. I have always myself felt the greatest difficulty 

 in believing in waves of heat coming first to this and then to 

 that quarter of the world : I suspect the heat plays quite a 



1 The paper was sent in MS., and seems not to have been published. 

 Mr. Woodd was connected by marriage with Mr. Darwin's cousin, the 

 late Rev. W. Darwin Fox. It was perhaps in consequence of this that 

 Mr. Darwin proposed Mr. Woodd for the Geological Society. 



