302 Rev. Dr. Irving — On Dynamic Metamorphism. 



into such intimate contact as to bring them within the field of its 

 operation.^ This, too, seems to be Spring's own interpretation of 

 the results obtained.^ 



A case, the exact reverse of that of Cu S, has been established by 

 the more recent work of Dr. Spring in conjunction with Van't Hoff.^ 

 The substance acted upon was the double acetate of copper and lime. 

 The formula for this double acetate is Cu (0211302)2 -j-Oa (0311302)2 

 +8H3O, and it occurs as 8-sided prisms of the quadratic system. 

 It is gradually built up with the aid of moderate external heat by 

 adding gradually free acetic acid to a warmed mixture of equivalent 

 proportions of neutral acetate of copper and slaked lime in water.* 

 The process is a complicated one ; but it is not reversible, for in the 

 experiment referred to the double acetate is resolved by a pressure 

 of 7000 atmospheres into the two separate acetates of copper and 

 lime with the separation-out of some of the water of constitution, 

 the same change in fact as is effected by heating the salt above 

 75° 0. at ordinary atmospheric pressure. The effect of pressure 

 here is again to effect a transformation which is accompanied by 

 loss of volume ; tending to give greater closeness to the atoms until 

 they obtain that configuration which belongs to their most stable 

 relation. We may compare it with the action of heat in breaking 

 up the molecules of ammonium nitrate to such an extent as to allow 

 the atoms to rearrange themselves (with evolution of heat) in the 

 more stable compounds N2O and HjO. The fact is one which, taken 

 along with the. case of Cu S, is of far-reaching significance, but 

 cannot be followed up further here. So far as it goes, it lends 

 support to a * diagenetic ' rather than to an ' epigenetic ' theory of 

 metamorphism.* 



Mr. Harker misrepresents me, when he suggests that I have 

 assumed that "the whole of the work done in the compression, 

 deformation, and friction of rocks passes into heat." I have never 

 assumed anything so nonsensical, as Mr. Harker may see, if he will 

 do me the favour of making a more intimate acquaintance with my 

 little work, to which he refers. Neither he nor 1 was dealing with 

 a case of ' deformation,' but with a hypothetical case of what Heini 

 calls ' iiberlastet,' the condition, that is to say, of ' latent plasticity ' 

 antecedently to deformation, where the burden upon the deep-seated 

 rock-mass produces hydrostatic pressure greater than the internal 

 resistance to deformation which the cohesion can offer. All that 



1 This was pointed out by me in App. ii. note D of my original thesis written in 

 1887 (see " Chem. and Phys. Studies," etc., p. 108). 



2 See "Am. Journ. Sci." vol. xxxv. (1888) p. 78, and vol. xxxvi. (1888) p. 285, 

 et seq. I am much obliged to General MacMahon for furnishing me with these 

 references. 



^ See " Zeitschrift fiir physik. Chemie," i. 5, cited in ' Nature,' vol. xxxvi. p. 160. 



* Wislicenus, " Organische Chemie," pp. 541, 542. 



5 From certain known facts, it does not seem at all improbable that such complex 

 syntheses may have taken place extensively in the early stages of the genesis of 

 rock-forming minerals. Among them I have suggested (" Chem. and Phys. Studies," 

 etc., App. ii. note Q,) the formation of minerals of the spinel type, in which AljOj 

 plays the part of an acid, the alumina being set free with subsequent alteration of 

 physical conditions, to enter into new relations as a base. 



