Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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The Phenomenon Of
A Basaltic Rock Containing Masses Of Indurated Marl Split Into
Small Columns, Is Also Found In The
Mittelgebirge, in Bohemia.
Visiting those countries in 1792, in company with Mr. Freiesleben,
we even recognized in the marl of
The Stiefelberg the imprint of a
plant nearly resembling the Cerastium, or the Alsine. Are these
strata, contained in the trappean mountains, owing to muddy
irruptions, or must we consider them as sediments of water, which
alternate with volcanic deposits? This last hypothesis seems so
much the less admissible, since, from the researches of Sir James
Hall on the influence of pressure in fusions, the existence of
carbonic acid in substances contained in basalt presents nothing
surprising. Several lavas of Vesuvius present similar phenomena. In
Lombardy, between Vicenza and Albano, where the calcareous stone of
the Jura contains great masses of basalt, I have seen the latter
enter into effervescence with the acids wherever it touches the
calcareous rock.
We had not time to reach the summit of a hill very remarkable for
having its base formed of banks of clay under strata of basalt,
like a mountain in Saxony, called the Scheibenbergen Hugel, which
is become celebrated on account of the disputes of volcanean and
neptunean geologists. These basalts were covered with a mammiform
substance, which I vainly sought on the Peak of Teneriffe, and
which is known by the names of volcanic glass, glass of Muller, or
hyalite: it is the transition from the opal to the chalcedony.
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