Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 3 - By Alexander Von Humboldt And Aime Bonpland.
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In These Parts Nothing Seems To
Indicate A Process Of Formation Likely To Be Renewed In Our Days.
The
slaty rock exhibits no open cleft; and none is found parallel with the
direction of the slates.
It may also be inquired whether this
aluminous slate be a transition-formation lying on the primitive
mica-slate of Araya, or whether it owe its origin merely to a change
of composition and texture in the beds of mica-slate. I lean to the
latter proposition; for the transition is progressive, and the
clay-slate (thonschiefer) and mica-slate appear to me to constitute
here but one formation. The presence of cyanite, rutile-titanite, and
garnets, and the absence of Lydian stone, and all fragmentary or
arenaceous rocks, seem to characterise the formation we describe as
primitive. It is asserted that even in Europe ampelite and green stone
are found, though rarely, in slates anterior to transition-slate.
When, in 1785, after an earthquake, a great rocky mass was broken off
in the Aroyo del Robalo, the Guaykeries of Los Serritos collected
fragments of alum five or six inches in diameter, extremely pure and
transparent. It was sold in my time at Cumana to the dyers and
tanners, at the price of two reals* per pound, while alum from Spain
cost twelve reals. (* The real is about 6 1/2 English pence.) This
difference of price was more the result of prejudice and of the
impediments to trade, than of the inferior quality of the alum of the
country, which is fit for use without undergoing any purification.
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