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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After The Limestone
And Gypseous Formations, There Would Remain To Be Examined, Among
The Secondary Rocks, A Third Formation, That
Of the argillaceous
sandstone, newer than the brine-spring formations; but this rock,
composed of small grains of quartz cemented
By clay, seldom
contains caverns; and when it does, they are not extensive.
Progressively narrowing towards their extremity, their walls are
covered with a brown ochre.
We have just seen, that the form of grottoes depends partly on the
nature of the rocks in which they are found; but this form,
modified by exterior agents, often varies even in the same
formation. The configuration of caverns, like the outline of
mountains, the sinuosity of valleys, and so many other phenomena,
present at first sight only irregularity and confusion. The
appearance of order is resumed, when we can extend our observations
over a vast space of ground, which has undergone violent, but
periodical and uniform revolutions. From what I have seen in the
mountains of Europe, and in the Cordilleras of America, caverns may
be divided, according to their interior structure, into three
classes. Some have the form of large clefts or crevices, like veins
not filled with ore; such as the cavern of Rosenmuller, in
Franconia, Elden-hole, in the peak of Derbyshire, and the Sumideros
of Chamacasapa in Mexico. Other caverns are open to the light at
both ends. These are rocks really pierced; natural galleries, which
run through a solitary mountain: such are the Hohleberg of
Muggendorf, and the famous cavern called Dantoe by the Ottomite
Indians, and the Bridge of the Mother of God, by the Mexican
Spaniards.
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