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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Between Nueva Barcelona and the Cerro del Bergantin a quartzose
sandstone covers the Jura limestone of Cumanacoa.
Is it an arenaceous
rock analogous to green sandstone, or does it belong to the sandstone
of Cocollar? In the latter case its presence seems to prove still more
clearly that the limestones of Cumanacoa and Caripe are only two parts
of the same system, alternating with sandstone, sometimes quartzose,
sometimes slaty.
10. GYPSUM OF THE LLANOS OF VENEZUELA.
Deposits of lamellar gypsum, containing numerous strata of marl, are
found in patches on the steppes of Caracas and Barcelona; for
instance, in the table-land of San Diego, between Ortiz and the Mesa
de Paja; and near the mission of Cachipo. They appeared to me to cover
the Jura limestone of Tisnao, which is analogous to that of Caripe,
where we find it mixed with masses of fibrous gypsum. I have not given
the name formation either to the sandstone of the Orinoco, of
Cocollar, of Bergantin or to the gypsum of the Llanos, because nothing
as yet proves the independence of those arenaceous and gypsous soils.
I think it will one day be ascertained that the gypsum of the Llanos
covers not only the Jura limestone of the Llanos, but that it is
sometimes enclosed in it like the gypsum of the Golfo Triste on the
east of the Alpine limestone of Cumanacoa. The great masses of sulphur
found in the layers, almost entirely clayey, of the steppes (at
Guayuta, valley of San Bonifacio, Buen Pastor, confluence of the Rio
Pao with the Orinoco) may possibly belong to the marl of the gypsum of
Ortiz. These clayey beds are more worthy of attention since the
interesting observations of Von Buch and several other celebrated
geologists respecting the cavernosity of gypsum, the irregularity of
the inclination of its strata and its parallel position with the two
declivities of the Hartz and the upheaved chain of the Alps; while the
simultaneous presence of sulphur, oligist iron and the sulphurous acid
vapours which precede the formation of sulphuric acid, seem to
manifest the action of forces placed at a great depth in the interior
of the globe.
11. FORMATION OF MURIATIFEROUS CLAY (WITH BITUMEN AND LAMELLAR GYPSUM)
OF THE PENINSULA OF
ARAYA.
This soil presents a striking analogy with salzthon or leberstein
(muriatiferous clay) which I have found accompanying gem-salt in every
zone. In the salt-pits of Araya (Haraia) it attracted the attention of
Peter Martyr d'Anghiera at the beginning of the sixteenth century. It
probably facilitated the rupture of the earth and the formation of the
gulf of Cariaco. This clay is of a smoky colour, impregnated with
petroleum, mingled with lamellar and lenticular gypsum and sometimes
traversed by small veins of fibrous gypsum. It incloses angular and
less friable masses of dark brown clay with a slaty and sometimes
conchoidal fracture. Muriate of soda is found in particles invisible
to the naked eye. The relations of position or superposition between
this soil and the tertiary rocks does not appear sufficiently clear to
enable me to pronounce with certainty on this element, the most
important of positive geology. The co-ordinate layers of gem-salt,
muriatiferous clay and gypsum present the same difficulties in both
hemispheres; these masses, the forms of which are very irregular,
everywhere exhibit traces of great commotions. They are scarcely ever
covered by independent formations; and after having been long
believed, in Europe, that gem-salt was exclusively peculiar to Alpine
and transition limestone, it is now still more generally admitted,
either from reasoning founded on analogy or from suppositions on the
prolongation of the strata, that the true location of gem-salt is
found in variegated sandstone (buntersandstein). Sometimes gem-salt
appears to oscillate between variegated sandstone and muschelkalk.
I made two excursions on the peninsula of Araya. In the first I was
inclined to consider the muriatiferous clay as subordinate to the
conglomerate (evidently of tertiary formation) of the Barigon and of
the mountain of the castle of Cumana, because a little to the north of
that castle I had found shelves of hardened clay containing lamellar
gypsum inclosed in the tertiary strata. I believed that the
muriatiferous clay might alternate with the calcareous conglomerate of
Barigon; and near the fishermen's huts situated opposite Macanao,
conglomerate rocks appeared to me to pierce through the strata of
clay. During a second excursion to Maniquarez and the aluminiferous
slates of Chaparuparu, the connexion between tertiary strata and
bituminous clay seemed to me somewhat problematical. I examined more
particularly the Penas Negras near the Cerro de la Vela,
east-south-east of the ruined castle of Araya. The limestone of the
Penas is compact, bluish grey and almost destitute of petrifactions.
It appeared to me to be much more ancient than the tertiary
conglomerate of Barigon, and I saw it covering, in concordant
position, a slaty clay, somewhat analogous to muriatiferous clay. I
was greatly interested in comparing this latter formation with the
strata of carburetted marl contained in the Alpine limestone of
Cumanacoa. According to the opinions now most generally received, the
rock of the Penas Negras may be considered as representing muschelkalk
(limestone of Gottingen); and the saliferous and bituminous clay of
Araya, as representing variegated sandstone; but these problems can
only be solved when the mines of those countries are worked. Those
geologists who are of opinion that the gem-salt of Italy penetrates
into a stratum above the Jura limestone, and even the chalk, may be
led to mistake the limestone of the Penas Negras for one of the strata
of compact limestone without grains of quartz and petrifactions, which
are frequently found amidst the tertiary conglomerate of Barigon and
of the Castillo de Cumana; the saliferous clay of Araya would appear
to them analogous to the plastic clay of Paris,* (* Tertiary sandstone
with lignites, or molassus of Argovia.) or to the clayey shelves (dief
et tourtia) of secondary sandstone with lignites, containing
salt-springs, in Belgium and Westphalia.
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