SALMON — RESEARCHES ON PSEUDOMORPHS. 



17 



circumstance which should surprise us, for kyanite is found especially 

 in rocks which are very rich in mica ; moreover, the mica which 

 penetrates it is completely identical with that of the mica-schist in 

 which it is formed. It is, therefore, very plain that the mica and the 

 kyanite were crystallized simultaneously, and at the same time as the 

 rock which incloses them. 



The same remark applies to andalusite, to chiastolite, to staurolite, 

 to hornblende, to augite, &c, which are often more or less penetrated 

 by the micas. In the very numerous specimens I have examined, 

 the various minerals were not pseudomorphosed ; they simply en- 

 veloped the micas, which were identical with those of the rocks in 

 which they were formed. 



The largely lamellar chlorite, which in chlorite-schist envelopes 

 and penetrates, often in the most intimate manner, crystals of mag- 

 netite, and which does not differ from that which constitutes the 

 chloritic schist itself, does not seem to me to result any the more from 

 a pseudomorphism. 



I am inclined to believe that it will be necessary to make pretty 

 numerous suppressions among the minerals which are regarded as 

 pseudomorphic, and particularly among the silicates. The only 

 pseudomorphic which should be retained are those which take the 

 form of another, and which are, besides, susceptible of replacing it 

 completely. It is, moreover, easy to understand that when minerals 

 have crystallized simultaneously, they were in a position to associate 

 and'envelope themselves in easy proportion ; which, indeed, before long- 

 will become still more evident. 



2nd, Envelopment with Symmetrical Arrangement. — Envelopment 

 is sometimes accompanied by symmetrical arrangement, and then it 

 is necessary again to distinguish many cases. 



Symmetrical arrangement is observed, in its rudimentary state, 

 whenever the two minerals are grouped in respect to each other with 

 a certain symmetry. This, for example, is what seems to occur in 

 the galena of Neudorf, in the Harz, which forms a thick and more or 

 less regular crust around calcite. According to Messrs. Scheerer 

 and Blum, this galena is in very brilliant crystals, which attain the 

 size of a nut, and present combinations of the octohedron, the cube, 

 and the rhomboidal dodecahedron. It envelopes the calcite, and is 

 also enveloped by it. Its thickness is often reduced to that of a 

 sheet of paper. 



Garnet offers the same peculiarities at Arendal, at La Bergstrasse, 

 and at Le Canigou ; for its crystals envelope calcite which is likewise 

 crystallized, and the thickness of their sides may become microscopic. 

 Sometimes also a crystal of garnet envelopes pistacio- green epidote 

 (pistazite), which in its turn envelopes the calcite. Moreover, 

 garnet may similarly envelope felspar, quartz, hornblende, diallage, 

 gypsum, &c. 



The idocrase of Christiansand, which has formed in the saccarhoid 

 limestone, is in large crystals, which have only a few lines of thick- 

 ness, and which also envelope the calcite. 



VOL. iv. 0 c 



