The Cavity Containing The Lichen Was Found Closed On All Sides By Enormous Masses Of Stalactite.)

The caverns in mountains of gypsum often contain mephitic emanations and deleterious gases.

It is not the sulphate of lime that acts on the atmospheric air, but the clay slightly mixed with carbon, and the fetid limestone, so often mingled with the gypsum. We cannot yet decide, whether the swinestone acts as a hydrosulphuret, or by means of a bituminous principle.* (* That description of fetid limestone called by the German mineralogists stinkstein is always of a blackish brown colour. It is only by decomposition that it becomes white, after having acted on the surrounding air. The stinkstein which is of secondary formation, must not be confounded with a very white primitive granular limestone of the island of Thasos, which emits, when scraped, a smell of sulphuretted hydrogen. This marble is coarser grained than Carrara (Marmor lunense). It was frequently employed by the Grecian sculptors, and I often picked up fragments of it at the Villa Adriani, near Rome.) Its property of absorbing oxygen gas is known to all the miners of Thuringia. It is the same as the action of the carburetted clay of the gypseous grottoes, and of the great chambers (sinkwerke) dug in mines of fossil salt which are worked by the introduction of fresh water. The caverns of calcareous mountains are not exposed to those decompositions of the atmospheric air, unless they contain bones of quadrupeds, or the mould mixed with animal gluten and phosphate of lime, from which arise inflammable and fetid gases.

Though we made many enquiries among the inhabitants of Caripe, Cumanacoa, and Cariaco, we did not learn that they had ever discovered in the cavern of Guacharo either the remains of carnivorous animals, or those bony breccias of herbivorous animals, which are found in the caverns of Germany and Hungary, and in the clefts of the calcareous rocks of Gibraltar. The fossil bones of the megatherium, of the elephant, and of the mastodon, which travellers have brought from South America, have all been found in the light soil of the valleys and table-lands. Excepting the megalonyx,* a kind of sloth of the size of an ox, described by Mr. Jefferson, I know not a single instance of the skeleton of an animal buried in a cavern of the New World. (* The megalonyx was found in the caverns of Green Briar, in Virginia, at the distance of 1500 leagues from the megatherium, which resembles it very much, and is of the size of the rhinoceros.) The extreme scarcity of this geological phenomenon will appear the less surprising to us, if we recollect, that in France, England, and Italy, there are also a great number of grottoes in which we have never met with any vestige of fossil bones.

Although, in primitive nature, whatever relates to ideas of extent and mass is of no great importance, yet I may observe, that the cavern of Caripe is one of the most spacious known to exist in limestone formations. It is at least 900 metres or 2800 feet in length.* (* The famous Baumannshohle in the Hartz, according to Messrs. Gilbert and Ilsen, is only 578 feet in length; the cavern of Scharzfeld 350; that of Gaylenreuth 304; that of Antiparos 300. But according to Saussure, the Grotto of Balme is 1300 feet.) Owing to the different degrees of solubility in rocks, it is generally not in calcareous mountains, but in gypseous formations, that we find the most extensive succession of grottoes. In Saxony there are some in gypsum several leagues in length; for instance, that of Wimelburg, which communicates with the cavern of Cresfield.

The determination of the temperature of grottoes presents a field for interesting observation. The cavern of Caripe, situated nearly in the latitude of 10 degrees 10 minutes, consequently in the centre of the torrid zone, is elevated 506 toises above the level of the sea in the gulf of Cariaco. We found that, in every part of it, in the month of September, the temperature of the internal air was between 18.4 and 18.9 degrees of the centesimal thermometer; the external atmosphere being at 16.2 degrees. At the entrance of the cavern, the thermometer in the open air was at 17.6 degrees; but when immersed in the water of the little subterranean river, it marked, even to the end of the cavern, 16.8 degrees. These experiments are very interesting, if we reflect on the tendency to equilibrium of heat, in the waters, the air, and the earth. When I left Europe, men of science were regretting that they had not sufficient data on what is called the temperature of the interior of the globe; and it is but very recently that efforts have been made, and with some success, to solve the grand problem of subterranean meteorology. The stony strata that form the crust of our planet, are alone accessible to our examination; and we now know that the mean temperature of these strata varies not only with latitudes and heights, but that, according to the position of the several places, it performs also, in the space of a year, regular oscillations round the mean heat of the neighbouring atmosphere. The time is gone by when men were surprised to find, in other zones, the heat of grottoes and wells differing from that observed in the caves of the observatory at Paris. The same instrument which in those caves marks 12 degrees, rises in the subterraneous caverns of the island of Madeira, near Funchal, to 16.2 degrees; in Joseph's Well, at Cairo* to 21.2 degrees (* At Funchal (latitude 32 degrees 37 minutes) the mean temperature of the air is 20.4 degrees, and at Cairo (latitude 30 degrees 2 minutes), according to Nouet, it is 22.4 degrees.); in the grottoes of the island of Cuba to 22 or 23 degrees.* (* The mean temperature of the air at the Havannah, according to Mr. Ferrer, is 25.6 degrees.) This increase is nearly in proportion to that of the mean temperature of the atmosphere, from latitude 48 degrees to the tropics.

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