*
[footnote[ *Humboldt, 'Lettre a M. Brochant de Villiers', in the 'Annales
de Chimie et de Physique', t. xxiii., p. 261; Leop. von Buch, 'Geog. Briefe
uber das sudliche Tyrol', s. 101, 105, und 273.
Another mode of transformation occurs where all the strata of the compact
limestone have been changed into granular limestone by the action of
granite, and syenitic or dioritic porphyry.*
[footnote] *On the transformation of compact into granular limestone by the
action of granite, in the Pyrenees at the 'Montagnes de Rancie', see
Dufrenoy, in the 'Memoires Geologiques', t. ii., p. 440; and on similar
changes in the 'Montagnes de l'Oisans', see Elie de Beaumont, in the 'Mem.
Geolog.', t. ii., p. 379-415; on a similar effect produced by the action of
dioritic and pyroxenic porphyry (the 'ophite' described by Elie de Beaumont,
in the 'Geologie de la France', t. i., p. 72), between Tolosa and St.
Sebastian, see Dufrenoy, in the 'Mem. Geolog.', t. ii., p. 130; and by
syenite in the Isle of Skye, where the fossils in the altered limestone may
still be distinguished, see Von Dechen, in his 'Geognosie', p. 573. In the
transformation of chalk by contact with basalt, the transposition of the
most minute particles in the processes of crystallization and granulation is
the more remarkable, because the excellent microscopic investigations of
Ehrenberg have shown that the particles of chalk previously existed in the
form of closed rings.
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