330 



NATURE 



[Fed. 22, 1872 



different ; and I have believed, and still believe, that ex- 

 tended beds of rock have been turned into this mineral 

 by a method analo,c;ous to that wh-ch takes place in 

 pseudomorphism. Had Mr. Hunt's statement been made 

 a special one, restricted to this case, 1 should have had 

 little objection to it. I may add that the method of origin 

 for serpentine which I have deemed most probable 

 (though perhaps not the only method) is one which he 

 once advocated — that of the alteration of beds of dolo- 

 mite, or magnesian carbonate of lime, by waters contain- 

 ing alkaline silicates in solution ; and it has appeared to 

 me that the facts (i) that serpentine is commonly asso- 

 ciated with beds of limestone or dolomite, (2) that chry- 

 solite crystals are sometimes found in these rocks, and 

 (3) that the forms of crystals of both dolomite and chryso- 

 lite occur among serpentine pseudumorphs, give strong 

 support to this view. 



Prof Hunt's opinion on this point in 1857 he thus ex- 

 pressed in a letter to the writer, sent for insertion in " Sil- 

 liman's Journal," where it appears in volume xxiii. (1857) 

 at p. 437, as a conclusion to his brief statement. 



"Suppose a solution of alkaline silicate, which will 

 never be wanting among sediments where feldspar exists, 

 to be diffused through a mixture of siliceous matter and 

 earthy carbonate, and we have, with a temperature of 

 212° F., and perhaps less, all the cimditions necessary for 

 the conversion of the sedimentary ma«s into pyroxenite, 

 diallage, serpentine, talc, rhodonite, all of which constitute 

 beds in our metamornhic strata. Add to the above the 

 presence of aluminous matter, and you have the elements 

 of chlorite, garnet, and epidote. We have here an ex- 

 planation of the metamorphism of the Silurian strata of 

 the Green Mountain range, and I believe of rock meta- 

 morphism in general." Again, in a letter dated July 6th, 

 published in volume xxiv., at page 272, he says : 



" I have already in a previous note indicated the manner 

 in which I suppose these siliceous and argillaceous mag- 

 nesites and dolomites to have been in certain parts of the 

 formation transformed by the intervention of solutions of 

 alkaline carbonates into silicates, such as talc, serpentine, 

 chlorilc, pyroxenite, &c. A further development of my 

 views of the metamorphism of sediments, with the results 

 of the investigation of a great many altered rocks, will 

 appear in the Report of Progress of the Geological Sur- 

 vey of Canada for the last three years — now in press." 



It should be added, that Prof. Hunt acknowledges his 

 change of opinion in his address. But, in view of it, some 

 moderating of his positiveness of assertion would have 

 been reasonable. 



4. That he attributes the origin of beds of serpentine 

 and steatite, — here following nearly Delesse, — to the 

 alteration of beds of different hydrous magnesian silicates 

 related to sepiolite (meerschaum), formed in the surface 

 ■waters of an era— Palxozoic or earlier — while fossiliferous 

 rocks were in progress : — when, as a matter of fact, no 

 such scpiolite-like beds are known to occur anywhere in 

 nnalterui stratified formations of Palaeozoic orpre-Silurian 

 time, and they are found of limited extent only in some strata 

 of comparatively recent origin. The hypothesis, although 

 deserving of consideration, is therefore without any solid 

 foundation. The doubts that have been recently thrown 

 about the Eozoon affect unfavourably the hypothesis, 

 since these supposed fossils have been made prominent in 

 its support. The view, if true, would, as Prof Hunt 

 implies, bring the making of serpentine and steatite rocks 

 under the kind of metamorphism styled by Giimbel 

 diagenesis, instead of that of epigenesis ; making them a 

 result of change without an addition of ingredients from 

 any external soiirce, like most other metamorphism, 

 instead of through the agency of outside ingredients. But 

 it wants facts to rest upon. 



5. That he attributes an origin similar to that for ser- 

 pentine and talc to beds of chlorite and hornblende ; 

 notwithstanding the fact that chlorite schist and horn- 



blende schist — the purest forms of any large beds of these 

 minerals— are .always more or less impure, and often 

 graduate into clay slate on one side, and mica schist on 

 the other ; and that these schists are thus so involved with 

 others, that if one is derived from ordinary sedimentary 

 beds, all must be. 



6. That he devotes some pages to a " theory of en- 

 velopment " as a method of accounting for the silicate 

 pseudomorphs referred to, beginning a paragraph with 

 the sentence : — 



" By far the greater number of cases on which this 

 general theory of pseudomorphism by a slov/ process of 

 alteration in minerals has been based, are, as I shall en- 

 deavour to show, examples of the phenomenon of mineral 

 envelopment, so well studied by Delesse in his essay on 

 Pseudomorphs." 



While, in fact, this theory has almost nothing to do with 

 the subject, since pseudomorphs of serpentine, steatite, 

 and other species, with regard to which there is the dis- 

 pute, consist often of pure serpentine, steatite, &c., and 

 therefore have no envelopcr, and are not cases of en- 

 Aelopment. This theorj' supposes the material of the 

 so-called pseudomorph to be an impurity taken up into a 

 crystal in process of formation — a thing of common occur- 

 rence ; and, if satisfactory, would account for the want of 

 conformity between internal qualities and external form. 

 It is unfortunate for it that, as just shown, it does not 

 apply where it is wanted. 



7. That he makes Delesse the author of the "theory of 

 envelopment : " — when Delesse has not proposed any such 

 theory for cases of ordmary pseudomorphism, but has 

 simply commenced, and very judiciously, his work on 

 Pseudomorphs (1859) by distinguishing the examples of 

 mere impurity, or envelopment, in cr>-stallisation, in order 

 to clear the way for the actual facts ; and then gives a 

 long list of admitted pseudomorphs, including in it nearly 

 all lands so recognised by other authors, and all that 

 affect the question discussed by Prof Hunt ; serpen- 

 tine occurring in the list as forming pseudomorphs 

 after chrysolite, hornblende, garnet ; steatite after py- 

 roxene, hornblende, epidote, scapolite, mica, topaz, mag- 

 nesite, dolomite, &c. In his work on metamorphism 

 (1S61), Delesse takes back none of his views on pseudo- 

 morphism ; and in his late " Reviews of the Progress of 

 Geology," down to the last just out (1S71), he reiterates 

 the ordinary views with regard to pseudomorphism, and 

 mentions the occurrence of other pseudomorphs consisting 

 of talc, serpentine, &c. 



8. That he cites Naumann as sustaining the " theory of 

 envelopment :" — when this learned crystallographer and 

 mineralogist has only commended Delesse's chapter on 

 the envelopment of minerals in crystals, and presents in 

 his " Mineralogy" (the last edition of which, that of 1S71, 

 is now before me) the subject of pseudomorphism in the 

 usual way, with nothing whatever on the theory of en- 

 velopment ; and, under the description of the species 

 serpentine, he speaks of " large pseudomorphous crystals 

 of serpentine from Snarum which still contain a nucleus 

 of altered chrysolite." 



There is hence no foundation for Mr. Hunt's statement 

 that his views are " ably supported by Delesse," or any 

 occasion for the " no small pleasure " he derived from 

 Naumann's letter ; or any warrant for the remark (p. 47) 

 that Delesse and Naumann hold the "view" "that the 

 so-called cases of pseudomorphism, on which the theory 

 of metamorphism by alteration has been built, are, for the 

 most part, examples of association and envelopment, and 

 the result of a contemporaneous and original crystallisa- 

 tion." These men of science are not to be counted upon 

 for aid, countenance, or comfort ; though claimed as friends, 

 it has not been their fault, as they have always a'-owed 

 the opinions of Haidinger and the " many others." It is 

 a strange fact that, neither these claimed friends, nor the 

 many announced opponents, with one or two exceptions, 



