316 ORIGIN OF CRYSTALLINE ROCKS. [XIII. 



to add that these facts may also be explained in a manner altogether 

 different (peuvent aussi ^interpreter d'une mani&re toute di/drente) ; 

 and some savans of Germany, notably G. Rose, Haidinger, Blum, 

 G. Bischof, and Rammelsberg, have sought their explanation in 

 pseudomorphism. Their example has been followed by most min- 

 eralogists, etc." (pages 358, 359). 



That the "pseudomorphism" of the authors just named is 

 chemical alteration or epigenesis, it is not necessary to remind the 

 reader, who will now be able to judge whether it is Professor Dana 

 or myself who has misrepresented or misunderstood Delesse. Let 

 us, however, add that the long and somewhat diffuse memoir of the 

 latter, from which we have quoted, is wanting in unity of plan and 

 purpose, and that parts of it, if we may hazard a conjecture, seem 

 to have been written while he still inclined to the views of the 

 opposite school. From the table of pseudomorphs which he has 

 given, and from many passages in the text, it might be inferred that 

 he then held the notions of Rose, Haidinger, etc., which he else- 

 where, in the same paper, speaks of as being entirely different from 

 his own. The views of Delesse, about this time, underwent a great 

 change, which has a historic importance in connection with those 

 which I advocate. When, in 1857 and 1858, he published the first 

 and second parts of his admirable series of studies on metamor- 

 phism, Delesse held, in common with nearly every geologist of the 

 time, to the eruptive origin of serpentine and the related magnesian 

 rocks. Serpentine was then classed by him with other " trappean 

 rocks " ; and he elsewhere asserted that " granitic and trappean 

 rocks" undergo in certain cases a change near their contact with 

 the enclosing rock, by which they lose silica, alumina, and alkalies, 

 and acquire magnesia and water, being thus changed into a mag- 

 nesian silicate, which may take the form of saponite, serpentine, 

 talc, or chlorite (Ann. des Mines (5), XII. 509 ; XIII. 393, 415). It 

 would be difficult to state more distinctly the view, which he then 

 held, of the origin of these magnesian rocks and minerals by the 

 chemical alteration of plutonic (granitic and trappean) rocks. This 

 was in 1858, and in 1859 appeared the memoir on pseudomorpha, 

 already noticed, in which, in place of the theory of epigenic pseudo- 

 morphism, or chemical alteration of various mineral silicates, taught 

 by the German school, he brought forward, in explanation of the 

 facts upon which this was based, another theory, which was only an 

 extension of that already maintained by Scheerer ami mv-dt. 



It was not until 1861 that Delesse published the last part of his 



