1874.] 167 [Dana. 



Note on Metamorphism and Pseudomorphism, with refer- 

 ence to the Statements of Prof. T. Sterry Hunt at 

 the Meeting of this Society of the 4th of March last. 

 By James D. Dana. 



In the paper by Mr. Hunt, reviewing Dr. Genth's memoir on the 

 Corundum of North Carolina, the author makes statements respect- 

 ing my views on metamorphism and pseudomorphism, which do not 

 accord with my understanding of them, and I therefore present to 

 the Society this note on the subject. 



Mr. Hunt regards the so-called pseudomorphs among mineral sili- 

 cates as examples for the most part of replacement and " envelop- 

 ment." This word envelopment was taken from Delesse's paper on 

 pseudomorphism. It means, as used by Delesse, simply mixtures 

 produced by the crystallizing together of minerals. This author, 

 knowing that such mixtures might be mistaken for pseudomorphs, 

 commences his work — published in 1859 — with a chapter on 

 " Envelopment," or such mixtures, in order to clear the way for the 

 treatment of true pseudomorphs. He then takes up the subject of 

 pseudomorphs, and, after remarks on a number of the cases, gives a 

 long table, in which occur, on pages 55, 56, 67, the following pseudo- 

 morphs of silicates after silicates. 



Mica, after Orthoclase and Tourmaline. 



Okthoclase, after Laumontite, Prehnite, Analcite. 



Ice Spar (var. of Orthoclase) after Leucite. 



Gieseckite and Liebenerite, after Nephelite. 



Tourmaline, after Orthoclase. 



Steatite or Talc, after Pyroxene, Amphibole, Epidote, Couzeranite, 



Mica, Topaz, Pectolite, Analcite, Mesole. 

 Serpentine, after Amphibole, Chrysolite, Garnet. 

 Chlorite, after Garnet, Scapolite (Couzeranite), Axinite. 

 Pectolite, after Analcite. 



Prehnite, after Laumontite, Leonhardite, Analcite, Natrolite, Scolecite. 

 Analcite, after Laumontite. 

 Thomsonite, after Nephelite. 

 Scolecite, after Apophyllite. 



The table shows that Delesse does not class the above cases of 

 pseudomorphism among cases of envelopment; he, like all other 

 writers on pseudomorphism, makes them true pseudomorphs. Even 

 serpentine after hornblende and chrysolite, gieseckite after nephelite, 

 and mica after tourmaline, are included. The very same views are 



