At Monte Serrato, in the island of
Elba, according to Frederic Hoffman, and in Tuscany, according to Alexander
Brongniart, it is formed by contact with euphotide and serpentine.
[footnote] *The silica is not merely colored by peroxyd of iron, but is
accompanied by clay, lime, and potash. Rose, 'Reise', bd. ii., s. 187. On
the formation of jasper by the action of dioritic porphyry, augite, and by
persthene rock, see Rose, bd. ii., s. 169, 187, und 192. See, also, bd. i.,
s. 427, where there is a drawing of the porphyry spheres between which
jasper occurs, in the calcareous graywacke of Bogoslowsk, being produced by
the Plutonic influence of the augitic rock; bd. ii., s. 545; and likewise
Humboldt, 'Asie Centrale', t. i., p. 486.
The contact and Plutonic action of granite have sometimes made argillaceous
schist granular, as was observed by Gustav Rose and myself in the Altai
Mountains (within the fortress of Buchtarminsk),* and have transformed it
into a mass resembling granite, consisting of a mixture of feldspar and
mica, in which larger laminae of the latter were again imbedded.**
[footnote] *Rose, 'Reise nach dem Ural', bd. i., s. 586-588.
[footnote] **In respect to the volcanic origin of mica, it is important to
notice that crystals of mica are found in the basalt of the Bohemian
Mittelgebirge, in the lava that in 1822 was ejected from Vesuvius
(Monticelli, 'Storia del Vesuvio negli Anni 1821 e 1822', 99), and in
fragments of agrillaceous alte imbedded in scoriaceous basalt at Hohenfels,
not far from Gerolstein, in the Eifel (see Mitscherlich, in Leonhard,
'Basalt-Gebilde', s.
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