The valley of the Tuy has its 'gold mine,' like almost every part of America inhabited by whites, and backed by primitive mountains. I was assured, that in 1780, foreign gold-gatherers had been engaged in picking up grains of that metal, and had established a place for washing the sand in the Quebrada del Oro. An overseer of a neighbouring plantation had followed these indications; and after his death, a waistcoat with gold buttons being found among his clothes, this gold, according to the logic of the people here, could only have proceeded from a vein, which the falling in of the earth had rendered invisible. In vain I objected, that I could not, by the mere view of the soil, without digging a large trench in the direction of the vein, judge of the existence of the mine; I was compelled to yield to the desire of my hosts. For twenty years past the overseer's waistcoat had been the subject of conversation in the country. Gold extracted from the bosom of the earth is far more alluring in the eyes of the vulgar, than that which is the produce of agricultural industry, favoured by the fertility of the soil, and the mildness of the climate.
North-west of the Hacienda del Tuy, in the northern range of the chain of the coast, we find a deep ravine, called the Quebrada Seca, because the torrent, by which it was formed, loses its waters through the crevices of the rock, before it reaches the extremity of the ravine. The whole of this mountainous country is covered with thick vegetation. We there found the same verdure as had charmed us by its freshness in the mountains of Buenavista and Las Lagunetas, wherever the ground rises as high as the region of the clouds, and where the vapours of the sea have free access. In the plains, on the contrary, many trees are stripped of a part of their leaves during the winter; and when we descend into the valley of the Tuy, we are struck with the almost hibernal aspect of the country. The dryness of the air is such that the hygrometer of Deluc keeps day and night between 36 and 40 degrees. At a distance from the river scarcely any huras or piper-trees extend their foliage over thickets destitute of verdure. This seems owing to the dryness of the air, which attains its maximum in the month of February; and not, as the European planters assert, "to the seasons of Spain, of which the empire extends as far as the torrid zone." It is only plants transported from one hemisphere to the other, which, in their organic functions, in the development of their leaves and flowers, still retain their affinity to a distant climate: faithful to their habits, they follow for a long time the periodical changes of their native hemisphere. In the province of Venezuela the trees stripped of their foliage begin to renew their leaves nearly a month before the rainy season. It is probable, that at this period the electrical equilibrium of the air is already disturbed, and the atmosphere, although not yet clouded, becomes gradually more humid. The azure of the sky is paler, and the elevated regions are loaded with light vapours, uniformly diffused. This season may be considered as the awakening of nature; it is a spring which, according to the received language of the Spanish colonies, proclaims the beginning of winter, and succeeds to the heats of summer.* (* That part of the year most abundant in rain is called winter; so that in Terra Firma, the season which begins by the winter solstice, is designated by the name of summer; and it is usual to hear, that it is winter on the mountains, at the time when summer prevails in the neighbouring plains.)
Indigo was formerly cultivated in the Quebrada Seca; but as the soil covered with vegetation cannot there concentrate so much heat as the plains and the bottom of the Tuy valley receive and radiate, the cultivation of coffee has been substituted in its stead. As we advanced in the ravine we found the moisture increase. Near the Hato, at the northern extremity of the Quebrada, a torrent rolls down over sloping beds of gneiss. An aqueduct was being formed there to convey the water to the plain. Without irrigation, agriculture makes no progress in these climates. A tree of monstrous size fixed our attention.* (* Hura crepitans.) It lay on the slope of the mountain, above the house of the Hato. On the least dislodgment of the earth, its fall would have crushed the habitation which it shaded: it had therefore been burnt near its foot, and cut down in such a manner, that it fell between some enormous fig-trees, which prevented it from rolling into the ravine. We measured the fallen tree; and though its summit had been burnt, the length of its trunk was still one hundred and fifty-four feet.* (* French measure, nearly fifty metres.) It was eight feet in diameter near the roots, and four feet two inches at the upper extremity.
Our guides, less anxious than ourselves to measure the bulk of trees, continually pressed us to proceed onward and seek the 'gold mine.' This part of the ravine is little frequented, and is not uninteresting. We made the following observations on the geological constitution of the soil. At the entrance of the Quebrada Seca we remarked great masses of primitive saccharoidal limestone, tolerably fine grained, of a bluish tint, and traversed by veins of calcareous spar of dazzling whiteness. These calcareous masses must not be confounded with the very recent depositions of tufa, or carbonate of lime, which fill the plains of the Tuy; they form beds of mica-slate, passing into talc-slate.* (* Talkschiefer of Werner, without garnets or serpentine; not eurite or weisstein. It is in the mountains of Buenavista that the gneiss manifests a tendency to pass into eurite.) The primitive limestone often simply covers this latter rock in concordant stratification. Very near the Hato the talcose slate becomes entirely white, and contains small layers of soft and unctuous graphic ampelite.* (* Zeichenschiefer.) Some pieces, destitute of veins of quartz, are real granular plumbago, which might be of use in the arts. The aspect of the rock is very singular in those places where thin plates of black ampelite alternate with thin, sinuous, and satiny plates of a talcose slate as white as snow. It would seem as if the carbon and iron, which in other places colour the primitive rocks, are here concentrated in the subordinate strata.
Turning westward we reached at length the ravine of gold (Quebrada del Oro). On examining the slope of a hill, we could hardly recognize the vestige of a vein of quartz. The falling of the earth caused by the rains had changed the surface of the ground, and rendered it impossible to make any observation. Great trees were growing in the places where the gold-washers had worked twenty years before. It is probable that the mica-slate contains here, as near Goldcronach in Franconia, and in Salzburgh, auriferous veins; but how is it possible to judge whether they be worth the expense of being wrought, or whether the ore is only in nodules, and in the less abundance in proportion as it is rich? We made a long herborization in a thick forest, extending beyond the Hato, and abounding in cedrelas, browneas, and fig-trees with nymphaea leaves. The trunks of these last are covered with very odoriferous plants of vanilla, which in general flower only in the month of April. We were here again struck with those ligneous excrescences, which in the form of ridges, or ribs, augment to the height of twenty feet above the ground, the thickness of the trunk of the fig-trees of America. I found trees twenty-two feet and a half in diameter near the roots. These ligneous ridges sometimes separate from the trunk at a height of eight feet, and are transformed into cylindrical roots two feet thick. The tree looks as if it were supported by buttresses. This scaffolding however does not penetrate very deep into the earth. The lateral roots wind at the surface of the ground, and if at twenty feet distance from the trunk they are cut with a hatchet, we see gushing out the milky juice of the fig-tree, which, when deprived of the vital influence of the organs of the tree, is altered and coagulates. What a wonderful combination of cells and vessels exist in these vegetable masses, in these gigantic trees of the torrid zone, which without interruption, perhaps during the space of a thousand years, prepare nutritious fluids, raise them to the height of one hundred and eighty feet, convey them down again to the ground, and conceal, beneath a rough and hard bark, under inanimate layers of ligneous matter, all the movements of organic life!
I availed myself of the clearness of the nights, to observe at the plantation of Tuy two emersions of the first and third satellites of Jupiter. These two observations gave, according to the tables of Delambre, longitude 4 hours 39 minutes 14 seconds; and by the chronometer I found 4 hours 39 minutes 10 seconds. During my stay in the valleys of the Tuy and Aragua the zodiacal light appeared almost every night with extraordinary brilliancy. I had perceived it for the first time between the tropics at Caracas, on the 18th of January, after seven in the evening. The point of the pyramid was at the height of 53 degrees. The light totally disappeared at 9 hours 35 minutes (apparent time), nearly 3 hours 50 minutes after sunset, without any diminution in the serenity of the sky. La Caille, in his voyage to Rio Janeiro and the Cape, was struck with the beautiful appearance displayed by the zodiacal light within the tropics, not so much on account of its less inclined position, as of the greater transparency of the air.* (* The great serenity of the air caused this phenomenon to be remarked, in 1668, in the arid plains of Persia.) It may appear singular, that Childrey and Dominic Cassini, navigators who were well acquainted with the seas of the two Indies, did not at a much earlier period direct the attention of scientific Europe to this light, and its regular form and progress. Until the middle of the eighteenth century mariners were little interested by anything not having immediate relation to the course of a ship, and the demands of navigation.
However brilliant the zodiacal light in the dry valley of Tuy, I have observed it more beautiful still at the back of the Cordilleras of Mexico, on the banks of the lake of Tezcuco, eleven hundred and sixty toises above the surface of the ocean. In the month of January, 1804, the light rose sometimes to more than 60 degrees above the horizon. The Milky Way appeared to grow pale compared with the brilliancy of the zodiacal light; and if small, bluish, scattered clouds were accumulated toward the west, it seemed as if the moon were about to rise.
I must here relate another very singular fact. On the 18th of January, and the 15th of February, 1800, the intensity of the zodiacal light changed in a very perceptible manner, at intervals of two or three minutes. Sometimes it was very faint, at others it surpassed the brilliancy of the Milky Way in Sagittarius. The changes took place in the whole pyramid, especially toward the interior, far from the edges. During these variations of the zodiacal light, the hygrometer indicated considerable dryness. The stars of the fourth and fifth magnitude appeared constantly to the naked eye with the same degree of light. No stream of vapour was visible: nothing seemed to alter the transparency of the atmosphere. In other years I saw the zodiacal light augment in the southern hemisphere half an hour before its disappearance. Cassini admitted "that the zodiacal light was feebler in certain years, and then returned to its former brilliancy." He thought that these slow changes were connected with "the same emanations which render the appearance of spots and faculae periodical on the solar disk." But this excellent observer does not mention those changes of intensity in the zodiacal light which I have several times remarked within the tropics, in the space of a few minutes. Mairan asserts, that in France it is common enough to see the zodiacal light, in the months of February and March, mingling with a kind of Aurora Borealis, which he calls 'undecided,' and the nebulous matter of which spreads itself all around the horizon, or appears toward the west. I very much doubt, whether, in the observations I have been describing, there was any mixture of these two species of light. The variations in intensity took place at considerable altitudes; the light was white, and not coloured; steady, and not undulating. Besides, the Aurora Borealis is so seldom visible within the tropics, that during five years, though almost constantly sleeping in the open air, and observing the heavens with unremitting attention, I never perceived the least traces of that phenomenon.
I am rather inclined to think that the variations of the zodiacal light are not all appearances dependent on certain modifications in the state of our atmosphere. Sometimes, during nights equally clear, I sought in vain for the zodiacal light, when, on the previous night, it had appeared with the greatest brilliancy. Must we admit that emanations which reflect white light, and seem to have some analogy with the tails of comets, are less abundant at certain periods? Researches on the zodiacal light have acquired a new degree of interest since geometricians have taught us that we are ignorant of the real causes of this phenomenon. The illustrious author of "La Mecanique Celeste" has shown that the solar atmosphere cannot reach even the planet Mercury; and that it could not in any case display the lenticular form which has been attributed to the zodiacal light. We may also entertain the same doubts respecting the nature of this light, as with regard to that of the tails of comets. Is it in fact a reflected or a direct light?
We left the plantation of Manterola on the 11th of February, at sunrise. The road runs along the smiling banks of the Tuy; the morning was cool and humid, and the air seemed embalmed by the delicious odour of the Pancratium undulatum, and other large liliaceous plants. In our way to La Victoria, we passed the pretty village of Mamon or of Consejo, celebrated in the country for a miraculous image of the Virgin. A little before we reached Mamon, we stopped at a farm belonging to the family of Monteras. A negress more than a hundred years old was seated before a small hut built of earth and reeds. Her age was known because she was a creole slave. She seemed still to enjoy very good health. "I keep her in the sun" (la tengo al sol), said her grandson; "the heat keeps her alive." This appeared to us not a very agreeable mode of prolonging life, for the sun was darting his rays almost perpendicularly. The brown-skinned nations, blacks well seasoned, and Indians, frequently attain a very advanced age in the torrid zone. A native of Peru named Hilario Pari died at the extraordinary age of one hundred and forty-three years, after having been ninety years married.