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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The Tract Of Country Of Which I Am Here Describing The Geological
Constitution Is Distinguished By The Astonishing Regularity Observed
In The Direction Of The Strata Of Which The Rocks Of Different Eras
Are Composed.
I have already often pointed the attention of my readers
to a geognostic law, one of the few that can be verified by precise
measurements.
Occupied since the year 1792 by the parallelism, or
rather the loxodromism of the strata, examining the direction and
inclination of the primitive and transition beds, from the coast of
Genoa across the chain of the Bochetta, the plains of Lombardy, the
Alps of Saint Gothard, the table-land of Swabia, the mountains of
Bareuth, and the plains of Northern Germany, I was struck with the
extreme frequency, if not the uniformity, of the horary directions 3
and 4 of the compass of Freiberg (direction from south-west to
north-east). This research, which I thought might lead to important
discoveries relating to the structure of the globe, had then such
attractions for me that it was one of the most powerful incentives of
my voyage to the equator. My own observations, together with those of
many able geologists, convince me that there exists in no hemisphere a
general and absolute uniformity of direction; but that in regions of
very considerable extent, sometimes over several thousand square
leagues, we observe that the direction and (though more rarely) the
inclination have been determined by a system of particular forces. We
discover at great distances a parallelism (loxodromism) of the strata,
a direction of which the type is manifest amidst partial perturbations
and which often remains the same in primitive and transition strata. A
fact which must have struck Palasson and Saussure is that in general
the direction of the strata, even in those which are far distant from
the principal ridges, is identical with the direction of mountain
chains; that is to say, with their longitudinal axis.
Venezuela is one of the countries in which the parallelism of the
strata of gneiss-granite, mica-slate and clay-slate, is most strongly
marked. The general direction of these strata is north 50 degrees
east, and the general inclination from 60 to 70 degrees north-west.
Thus I observed them on a length of more than a hundred leagues, in
the littoral chain of Venezuela; in the stratified granite of Las
Trincheras at Porto Cabello; in the gneiss of the islands of the lake
of Valencia, and in the vicinity of the Villa de Cura; in the
transition-slate and greenstone on the north of Parapara; in the road
from La Guayra to the town of Caracas, and through all the Sierra de
Avila in Cape Codera; and in the mica-slate and clay-slate of the
peninsula of Araya. The same direction from north-east to south-west,
and this inclination to north-west, are also manifest, although less
decidedly, in the limestones of Cumanacoa at Cuchivano and between
Guanaguana and Caripe.
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