2IO GEOLOGY [Chap. IX 



Letter 543 quarter as strong as Mrs. Hooker : but that is a vain hope. 

 You must have had some very interesting work with 

 glaciers, etc. When will the glacier structure and motion 

 ever be settled! When reading Tyndall's 1 paper it seemed 

 to me that movement in the particles must come into play 

 in his own doctrine of pressure ; for he expressly states that 

 if there be pressure on all sides, there is no lamination. 

 I suppose I cannot have understood him, for I should have 

 inferred from this that there must have been movement 

 parallel to planes of pressure. 



Sorby 2 read a paper to the Brit. Assoc, and he comes 

 to the conclusion that gneiss, etc., may be metamorphosed 

 cleavage or strata ; and I think he admits much chemical 

 segregation along the planes of division. I quite subscribe 

 to this view, and should have been sorry to have been so 

 utterly wrong, as I should have been if foliation was identical 

 with stratification. 



I have been nowhere and seen no one, and really have 

 no news of any kind to tell you. I have been working away 

 as usual, floating plants in salt water inter alia, and confound 

 them, they all sink pretty soon, but at very different rates. 

 Working hard at pigeons, etc., etc. By the way, I have been 

 astonished at the differences in the skeletons of domestic 

 rabbits. I showed some of the points to Waterhouse, and 

 asked him whether he could pretend that they were not as 

 great as between species, and he answered, " They are a 

 great deal more." How very odd that no zoologist should 

 ever have thought it worth while to look to the real structure 

 of varieties. . . . 



1 Prof. Tyndall had published papers " On Glaciers," and " On some 

 Physical Properties of Ice" (Proc. R. Inst., 1854-58) before the date 

 of this letter. In 1856 he wrote a paper entitled " Observations on 'The 

 Theory of the Origin of Slaty Cleavage,' by H. C. Sorby." Phil. Mag., 

 XII., 1856, p. 129. 



2 "On the Microscopical Structure of Mica-schist :" Brit. Ass. Rep., 

 1856, p. 78. See also Letters 540 — 542. 



