Struck With This Phenomenon, I Gathered At Higuerote A Considerable Quantity Of Branches And Roots, For The Purpose Of Making Some Experiments On The Infusion Of The Mangrove, On My Arrival At Caracas.

The infusion in warm water had a brown colour and an astringent taste.

It contained a mixture of extractive matter and tannin. The rhizophora, the mistletoe, the cornel-tree, in short, all the plants which belong to the natural families of the lorantheous and the caprifoliaceous plants, have the same properties. The infusion of mangrove-wood, kept in contact with atmospheric air under a glass jar for twelve days, was not sensibly deteriorated in purity. A little blackish flocculent sediment was formed, but it was attended by no sensible absorption of oxygen. The wood and roots of the mangrove placed under water were exposed to the rays of the sun. I tried to imitate the daily operations of nature on the coasts at the rise of the tide. Bubbles of air were disengaged, and at the expiration of ten days they formed a volume of thirty-three cubic inches. They were a mixture of azotic gas and carbonic acid. Nitrous gas scarcely indicated the presence of oxygen.* (* In a hundred parts there were eighty-four of nitrogen, fifteen of carbonic acid gas that the water had not absorbed, and one of oxygen.) Lastly, I set the wood and the roots of the mangrove thoroughly wetted, to act on a given volume of atmospheric air in a phial with a ground-glass stopple. The whole of the oxygen disappeared; and, far from being superseded by carbonic acid, lime-water indicated only 0.02. There was even a diminution of the volume of air, more than correspondent with the oxygen absorbed. These slight experiments led me to conclude that it is the moistened bark and wood which act upon the atmosphere in the forests of mangrove-trees, and not the water strongly tinged with yellow, forming a distinct band along the coasts. In pursuing the different stages of the decomposition of the ligneous matter, I observed no appearance of a disengagement of sulphuretted hydrogen, to which many travellers attribute the smell perceived amidst mangroves. The decomposition of the earthy and alkaline sulphates, and their transition to the state of sulphurets, may no doubt favour this disengagement in many littoral and marine plants; for instance, in the fuci: but I am rather inclined to think that the rhizophora, the avicennia, and the conocarpus, augment the insalubrity of the air by the animal matter which they contain conjointly with tannin. These shrubs belong to the three natural families of the Lorantheae, the Combretaceae, and the Pyrenaceae, in which the astringent principle abounds; this principle accompanies gelatin, even in the bark of beech, alder, and nut-trees.

Moreover, a thick wood spreading over marshy grounds would diffuse noxious exhalations in the atmosphere, even though that wood were composed of trees possessing in themselves no deleterious properties. Wherever mangroves grow on the sea-shore, the beach is covered with infinite numbers of molluscs and insects. These animals love shade and faint light, and they find themselves sheltered from the shock of the waves amid the scaffolding of thick and intertwining roots, which rises like lattice-work above the surface of the waters. Shell-fish cling to this lattice; crabs nestle in the hollow trunks; and the seaweeds, drifted to the coast by the winds and tides, remain suspended on the branches which incline towards the earth. Thus, maritime forests, by the accumulation of a slimy mud between the roots of the trees, increase the extent of land. But whilst these forests gain on the sea, they do not enlarge their own dimensions; on the contrary, their progress is the cause of their destruction. Mangroves, and other plants with which they live constantly in society, perish in proportion as the ground dries and they are no longer bathed with salt water. Their old trunks, covered with shells, and half-buried in the sand, denote, after the lapse of ages, the path they have followed in their migrations, and the limits of the land which they have wrested from the ocean.

The bay of Higuerote is favourably situated for examining Cape Codera, which is there seen in its full extent seven miles distant. This promontory is more remarkable for its size than for its elevation, being only about two hundred toises high. It is perpendicular on the north-west and east. In these grand profiles the dip of the strata appears to be distinguishable. Judging from the fragments of rock found along the coast, and from the hills near Higuerote, Cape Codera is not composed of granite with a granular texture, but of a real gneiss with a foliated texture. Its laminae are very broad and sometimes sinuous.* (* Dickflasriger gneiss.) They contain large nodules of reddish feldspar and but little quartz. The mica is found in superposed lamellae, not isolated. The strata nearest the bay were in the direction of 60 degrees north-east, and dipped 80 degrees to north-west. These relations of direction and of dip are the same at the great mountain of the Silla, near Caracas, and to the east of Maniquarez, in the isthmus of Araya. They seem to prove that the primitive chain of that isthmus, after having been ruptured or swallowed up by the sea along a space of thirty-five leagues,* (* Between the meridians of Maniquarez and Higuerote.) appears anew in Cape Codera, and continues westward as a chain of the coast.

I was assured that, in the interior of the earth, south of Higuerote, limestone formations are found. The gneiss did not act upon the magnetic needle; yet along the coast, which forms a cove near Cape Codera, and which is covered with a fine forest, I saw magnetic sand mixed with spangles of mica, deposited by the sea. This phenomenon occurs again near the port of La Guayra. Possibly it may denote the existence of some strata of hornblende-schist covered by the waters, in which schist the sand is disseminated. Cape Codera forms on the north an immense spherical segment.

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