The two parallel chains of Araya and the Cocollar were connected, to the east of the town of Cariaco, between the lakes of Campoma and Putaquao, by a kind of transverse dyke, which bears the name of Cerro de Meapire, and which in distant times, by resisting the impulse of the waves, has hindered the waters of the gulf of Cariaco from uniting with those of the gulf of Paria. Thus, in Switzerland, the central chain, that which passes by the Col de Ferrex, the Simplon, St. Gothard, and the Splugen, is connected on the north and the south with two lateral chains, by the mountains of Furca and Maloya. It is interesting to recall to mind those striking analogies exhibited in both continents by the external structure of the globe.
The primitive chain of Araya ends abruptly in the meridian of the village of Maniquarez; and the western slope of the peninsula, as well as the plains in the midst of which stands the castle of San Antonio, is covered with very recent formations of sandstone and clay mixed with gypsum. Near Maniquarez, breccia or sandstone with calcareous cement, which might easily be confounded with real limestone, lies immediately over the mica-slate; while on the opposite side, near Punta Delgada, this sandstone covers a compact bluish grey limestone, almost destitute of petrifactions, and traversed by small veins of calcareous spar. This last rock is analogous to the limestone of the high Alps.* (* Alpenkalkstein.)
The very recent sandstone formation of the peninsula of Araya contains:—first, near Punta Arenas, a stratified sandstone, composed of very fine grains, united by a calcareous cement in small quantity;—secondly, at the Cerro de la Vela, a schistose sandstone,* (* Sandsteinschiefer.) without mica, and passing into slate-clay,* (* Thonschiefer.) which accompanies coal;—thirdly, on the western side, between Punta Gorda and the ruins of the castle of Santiago, breccia composed of petrified sea-shells united by a calcareous cement, in which are mingled grains of quartz;—fourthly, near the point of Barigon, whence the stone employed for building at Cumana is obtained, banks of yellowish white shelly limestone, in which are found some scattered grains of quartz;—fifthly, at Penas Negras, at the top of the Cerro de la Vela, a bluish grey compact limestone, very tender, almost without petrifactions, and covering the schistose sandstone. However extraordinary this mixture of sandstone and compact limestone* (* Dichter kalkstein.) may appear, we cannot doubt that these strata belong to one and the same formation. The very recent secondary rocks everywhere present analogous phenomena; the molasse of the Pays de Vaud contains a fetid shelly limestone, and the cerite limestone of the banks of the Seine is sometimes mixed with sandstone.
The strata of calcareous breccia are composed of an infinite number of sea-shells, from four to six inches in diameter, and in part well preserved. We find they contain not ammonites, but ampullaires, solens, and terebratulae. The greater part of these shells are mixed: the oysters and pectinites being sometimes arranged in families. The whole are easily detached, and their interior is filled with fossil madrepores and cellepores. We have now to speak of a fourth formation, which probably rests* on the calcareous sandstone of Araya, I mean the muriatiferous clay. (* It were to be wished that mineralogical travellers would examine more particularly the Cerro de la Vela. The limestone of the Penas Negras rests on a slate-clay, mixed with quartzose sand; but there is no proof of the muriatiferous clay of the salt-works being of more ancient formation than this slate-clay, or of its alternating with banks of sandstone. No well having been dug in these countries, we can have no information respecting the superposition of the strata. The banks of calcareous sandstone, which are found at the mouth of the salt lake, and near the fishermen's huts on the coast opposite Cape Macano, appeared to me to lie beneath the muriatiferous clay.) This clay, hardened, impregnated with petroleum, and mixed with lamellar and lenticular gypsum, is analogous to the salzthon, which in Europe accompanies the sal-gem of Berchtesgaden, and in South America that of Zipaquira. It is generally of a smoke-grey colour, earthy, and friable; but it encloses more solid masses of a blackish brown, of a schistose, and sometimes conchoidal fracture. These fragments, from six to eight inches long, have an angular form. When they are very small, they give the clay a porphyroidal appearance. We find disseminated in it, as we have already observed, either in nests or in small veins, selenite, and sometimes, though seldom, fibrous gypsum. It is remarkable enough, that this stratum of clay, as well as the banks of pure sal-gem and the salzthon in Europe, scarcely ever contains shells, while the rocks adjacent exhibit them in great abundance.
Although the muriate of soda is not found visible to the eye in the clay of Araya, we cannot doubt of its existence. It shows itself in large crystals, if we sprinkle the mass with rain-water and expose it to the sun. The lagoon to the east of the castle of Santiago exhibits all the phenomena which have been observed in the salt lakes of Siberia, described by Lepechin, Gmelin, and Pallas. This lagoon receives, however, only the rain-waters, which filter through the banks of clay, and unite at the lowest point of the peninsula. While the lagoon served as a salt-work to the Spaniards and the Dutch, it did not communicate with the sea; at present this communication has been interrupted anew, by faggots placed at the place where the waters of the ocean made an irruption in 1726. After great droughts, crystallized and very pure muriate of soda, in masses of three or four cubic feet, is still drawn from time to time from the bottom of the lagoon. The salt waters of the lake, exposed to the heat of the sun, evaporate at their surface; crusts of salt, formed in a saturated solution, fall to the bottom; and by the attraction between crystals of a similar nature and form, the crystallized masses daily augment. It is generally observed that the water is brackish wherever lagoons are formed in clayey ground. It is true, that for the new salt-work near the battery of Araya, the seawater is received into pits, as in the salt marshes of the south of France; but in the island of Margareta, near Pampatar, salt is manufactured by employing only fresh water, with which the muriatiferous clay has first been lixiviated.
We must not confound the salt disseminated in these clayey soils with that contained in the sands of the seashore, on the coasts of Normandy. These phenomena, considered in a geognostical point of view, have scarcely any properties in common. I have seen muriatiferous clay at the level of the ocean at Punta Araya, and at two thousand toises' height in the Cordilleras of New Grenada. If in the former of these places it lies on very recent shelly breccia, it forms, on the contrary, in Austria near Ischel, a considerable stratum in the Alpine limestone, which, though equally posterior to the existence of organic life on the globe, is nevertheless of high antiquity, as is proved by the great number of rocks with which it is covered. We shall not question, that sal-gem, either pure or mixed with muriatiferous clay, may have been deposited by an ancient sea; but everything evinces that it was formed during an order of things bearing no resemblance to that in which the sea at present, by a slower operation, deposits a few particles of muriate of soda on the sands of our shores. In the same manner as sulphur and coal belong to periods of formation very remote from each other, the sal-gem is also found sometimes in transition gypsum,* (* Uebergangsgyps, in the transition slate of White Alley (l'Allee Blanche), and between the grauwacke and black transition limestone near Bex, below the Dent de Chamossaire, according to M. von Buch.) sometimes in the Alpine limestone,* (* At Halle in the Tyrol.) sometimes in a muriatiferous clay lying on a very recent sandstone,* (* At Punta Araya.) and lastly, sometimes in a gypsum* posterior to the chalk. (* Gypsum of the third formation among the secondary gypsums. The first formation contains the gypsum in which are found the brine-springs of Thuringia, and which is placed either in the Alpine limestone or zechstein, to which it essentially belongs (Freiesleben Geognost. Arbeiten tome 2 page 131), or between the zechstein and the limestone of the Jura, or between the zechstein and the new sandstone. It is the ancient gypsum of secondary formation of Werner's school (alterer flozgyps), which we almost preferably call muriatiferous gypsum. The second formation is composed of fibrous gypsum, placed either in the molasse or new sandstone, or between this and the upper limestone. It abounds in common clay, which differs essentially from the salzthon or muriatiferous clay. The third formation of gypsum is more recent than chalk. To this belongs the bony gypsum of Paris; and, as appears from the researches of Mr. Steffens (Geogn. Aufsatsze 1810 page 142), the gypsum of Segeberg, in Holstein, in which sal-gem is sometimes disseminated in very small nests (Jenaische Litteratur-Zeitung 1813 page 100). The gypsum of Paris, lying between a cerite limestone, which covers chalk and a sandstone without shells, is distinguished by fossil bones of quadrupeds, while the Segeberg and Lunebourg gypsums, the position of which is more uncertain, are characterized by the boracits which they contain. Two other formations, far anterior to the three we have just mentioned, are the transition gypsum (ubergangsgyps) of Aigle, and the primitive gypsum (urgyps) of the valley of Canaria, near Airolo. I flatter myself that I may render some service to those geologists who prefer the knowledge of positive facts to speculation on the origin of things, by furnishing them with materials from which they may generalize their ideas on the formation of rocks in both hemispheres. The relative antiquity of the formations is the principal object of a science which is to render us acquainted with the structure of the globe; that is to say, the nature of the strata which constitute the crust of our planet.)
The new salt-works of Araya have five reservoirs, or pits, the largest of which have two thousand three hundred square toises surface. Their mean depth is eight inches. Use is made both of the rain-water, which by filtration collects at the lowest part of the plain, and of the water of the sea, which enters by canals, or martellieres, when the flood-tide is favoured by the winds. The situation of these new salt-works is less advantageous than that of the lagoon. The waters which fall into the latter pass over steeper slopes, washing a greater extent of ground.
The earth already lixiviated is never carried away here, as it is from time to time in the island of Margareta; nor have wells been dug in the muriatiferous clay, with the view of finding strata richer in muriate of soda. The salineros, or salt-workers generally complain of want of rain; and in the new salt-works, it appears to me difficult to determine what quantity of salt is derived solely from the waters of the sea. The natives estimate it at a sixth of the total produce. The evaporation is extremely strong, and favoured by the constant motion of the air; so that the salt is collected in eighteen or twenty days after the pits are filled.
Though the muriate of soda is manufactured with less care in the peninsula of Araya than at the salt-works of Europe, it is nevertheless purer, and contains less of earthy muriates and sulphates. We know not whether this purity may be attributed to that portion of the salt which is furnished by the sea; for though it is extremely probable, that the quantity of salt dissolved in the waters of the ocean is nearly the same under every zone, it is not less uncertain whether the proportion between the muriate of soda, the muriate and sulphate of magnesia, and the sulphate and carbonate of lime, be equally invariable.
Having examined the salt-works, and terminated our geodesical operations, we departed at the decline of day to sleep at an Indian hut, some miles distant, near the ruins of the castle of Araya. Directing our course southward, we traversed first the plain covered with muriatiferous clay, and stripped of vegetation; then two chains of hills of sandstone, between which the lagoon is situated. Night overtook us while we were in a narrow path, bordered on one side by the sea, and on the other by a range of perpendicular rocks. The tide was rising rapidly, and narrowed the road at every step. We at length arrived at the foot of the old castle of Araya, where we enjoyed a prospect that had in it something lugubrious and romantic. The ruins stand on a bare and arid mountain, crowned with agave, columnar cactus, and thorny mimosas: they bear less resemblance to the works of man, than to those masses of rock which were ruptured at the early revolutions of the globe.