490 ADDRESS OF T. STERRY HUNT. 
lated silicate of magnesia, which sometimes accompanies serpen- - 
tine, results from the alteration of flint; while according to Rose, 
serpentine may even be produced from dolomite, which we are 
told is itself produced by the alteration of limestone. But this is 
not all, — feldspar may replace carbonate of lime, and carbonate 
of lime, feldspar, so that, according to Volger, some gneissoid lime- 
stones are probably formed from gneiss by the substitution of 
calcite for orthoclase. In this way, we dre led from gneiss or 
granite to limestone, from limestone to dolomite, and from dolo- 
mite to serpentine, or more directly from granite, granulite or 
diorite to serpentine at once, without passing through the inter- 
mediate stages of limestone and dolomite, till we are ready to 
exclaim in the words of Goethe : — 
“ Mich iingstigt das Verfingliche 
Im sAr a } PTY 
Won ichts verharret, Alles flieht, 
Wo schon verschwunden was man sieht,”* 
which we may thus translate : —‘“ I am vexed with the sophistry in 
their contrary jargon, where nothing endures, but all is fugitive, 
and where what we see has already passed away.” 
By far the greater number of cases on which this general theory 
of pseudomorphism by a slow process of alteration in minerals, has 
been based are, as I shall endeavor to show, examples of the phe- 
nomenon of mineral envelopment, so well studied by Delesse in 
his essay on Pseudomorphs,+ and may be considered under two 
heads :— first, that of symmetrical envelopment, in which one 
mineral species is so enclosed within the other that the two appear 
to form a single crystalline individual. Examples of this are seen 
when prisms of cyanite are surrounded by staurolite, or staurolite 
crystals completely enveloped in those of cyanite, the vertical axes 
of the two prisms corresponding. Similar cases are seen in the . 
enclosure of a prism of red in an envelope of green tourmaline, of 
allanite in epidote, and of various minerals of the pyroxene group 
in one another. The occurrence of muscovite in lepidolite, and 
of margarodite in lepidomelane, or the inverse, are well-known 
examples, and, according to Scheerer, the crystallization of serpen- 
tine around a nucleus of olivine is a similar case. This phenome 
non of symmetrical envelopment, as remarked by Delesse, shows 
arte ee RE 
*Chinesisch-Deutsche Jahres und Tages Zeiten, xi. 
t Annales des Mines, V, xvi, 317-392. 
Re ee EE eS 
ee ri te Pe 
Peter ta sea Fas ores 
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