In the valley of Irtysch, between Buchtarminsk and
Ustkamenogorsk, granite covers transition slate for a space of four miles,*
penetrating into it from above in narrow, variously ramified, wedge-like
veins.
[footnote] *Humboldt, 'Asie Centrale', t. i., p. 299-311, and the drawings
in Rose's 'Reise', bd. i., s. 611, in which we see the curvature in the
layers of granite which Leop. von Buch has pointed out as chracteristic.
I have only instanced these peculiarities in order to designate the
individual character of one of the most generally diffused erupted-rocks.
As granite is superposed on slate in Siberia and in the Departement de
Finisterre (Isle de Mihau), so it covers the Jura limestone in the mountains
of Oisons (Fermonts), and syenite, and indirectly also chalk, in Saxony,
near Weinbohla.*
[footnote] *This remarkable superposition was first described by Weiss in
Krsten's 'Archiv fur Bergbau und H?¬ttenwesen', bd. xvi., 1827, s. 5.
Near Mursinsk, in the Uralian district, granite is of a drusous character,
and here the pores, like the fissures and cavities of recent volcanic
products, inclose many kinds of magnificent crystals, especially beryls and
topazes.
2. 'Quartzose porphyry' is often found in the relation of veins to other
rocks.
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