244). On the formation of feldspar in argillaceous
schist, through contact with porphyry, occurring between Urval and Po?•et
(Forez), see Dufrenoy, in 'Geol. de la France', t. i., p. 137. It is
probably to a similar contact that certain schists near Paimpol, in
Brittany, with whose appearance I was much struck, while making a geological
pedestrian tour through that interesting country with Professor Kunth, owe
their amygdaloid and cellular character, t. i., p. 234.
Most geognosists adhere, with Leopold von Buch, to the well-known hypothesis
"that all the gneiss in the silurian strata of the transition formation,
between the Icy Sea and the Gulf of Finland, has been produced by the
metamorphic action of granite.*
[footnote] * Leopold von Buch, in the 'Abhandlungen der Akad. der
Wissenschaft zu Berlin, aus dem Jahr' 1842, s. 63, and in the 'Jahrbuchern
fur Wissenschaftliche Kritik Jahrg.' 1840, s. 196.
In the Alps, at St. Gothard, calcareous marl is likewise changed from
granite into mica slate, and then transformed into gneiss." Similar
phenomena of the formation of gneiss and mica slate through granite present
themselves in the oolitic group of the Tarantaise,* in which belemnites are
p 261
found in rocks, which have some claim to be considered as mica slate, and in
the schistose group in the western part of the island of Elba, near the
promontory of Calamita, and the Fichtelgebirge in Baireuth, between Loomitz
and Markleiten.
Pages:
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550