Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
- Page 121 of 777 - First - Home
He Discovered That Each Crystal
Of Pyroxene, Enveloped In The Earthy Mass, Is Separated From It By
Fissures Parallel To The Sides Of The Crystal.
These fissures seem to
be the effect of a contraction which the mass or basis of the
mandelstein has undergone.
I sometimes saw these balls of mandelstein
arranged in strata, and separated from each other by beds of grunstein
of ten or fourteen inches thick; sometimes (and this situation is most
common) the balls of mandelstein, two or three feet in diameter, are
found in heaps, and form little mounts with rounded summits, like
spheroidal basalt. The clay which separates these amygdaloid
concretions arises from the decomposition of their crust. They acquire
by the contact of the air a very thin coating of yellow ochre.
South-west of the village of Parapara rises the little Cerro de
Flores, which is discerned from afar in the steppes. Almost at its
foot, and in the midst of the mandelstein tract we have just been
describing, a porphyritic phonolite, a mass of compact feldspar of a
greenish grey, or mountain-green, containing long crystals of vitreous
feldspar, appears exposed. It is the real porphyrschiefer of Werner;
and it would be difficult to distinguish, in a collection of stones,
the phonolite of Parapara from that of Bilin, in Bohemia. It does not,
however, here form rocks in grotesque shapes, but little hills covered
with tabular blocks, large plates extremely sonorous, translucid on
the edges, and wounding the hands when broken.
Enter page number
PreviousNext
Page 121 of 777
Words from 32514 to 32764
of 211397
