Lively controversies and gross errors have prevailed concerning the geological formation of abysses. The abyss of Jean Nouveau, Vaucluse, among others, furnishes evidence against the false hypothesis that such pits are as a rule the results of cave-ins, whereas pits of that origin are rare and exceptional. These pits are for the most part fissures, the principal feature of which is their narrowness. At Jean Nouveau the greatest breadth is not more than about sixteen feet. It is the deepest vertical pit of a single shaft without intermediate terraces that we know of, and is about five hundred and thirty feet from the surface of the ground to its floor. The mass of stone rubbish at the bottom prevented our descending into a second pit.
Pits composed, like Vigne Close, of several successive wells, destroy another hypothesis—that of the formation of gouffres by the emissions from thermal springs.
The greatest danger in descending these pits arises from the showers of stones that sometimes come down upon the head of the explorer. These are often started by his friends the hunters, or by their dogs gamboling around at will.
While some of the caverns I have explored were stopped up by obstacles of one kind or another that prevented further progress, in others we found considerable rivers running a nearly free course. We rarely found pits formed by the collapse of the roofs of the cave in cases where the distance from the subterranean river which by its work of erosion provoked the catastrophe to the surface was more than one hundred metres. The pit of the Mas Raynal, Aveyron, is one hundred and six metres deep, and abuts upon a large subterranean river, which supplies the Sorgues of Saint-Affrique, one of the finest springs of France. When we explored it, in 1889, we could not pass the low chambers which occur in it because the water was too high, and we have not visited it since. Its exploration in a dry season might reveal many very interesting chambers.
In the cave of Rabanel, the first well, which ends in a talus of fallen stones, furnishes an instance of a vertical fissure grafted, if we may use the word, upon an interior grotto that already existed. A stream runs through this grotto which falls into a second well twenty-six metres, and is then lost in smaller passages so nearly stopped up with earth that we were not able to follow it through its course of about a mile till it comes out at the Brissac spring.
The cave of Trebiciano, in Istria, near Trieste, the deepest known, has a total depth of more than a thousand feet. It is not, however, entirely natural, but is composed of numerous vertical fissures which lead, at about eight hundred and fifty feet below the surface, to a large cavern, at the bottom of which flows the subterranean river Recca. The fissures do not naturally communicate directly with one another, but the engineer Lindner was commissioned in 1840-'41 by the city of Trieste to construct for the municipality a supply of potable water from the underground streams, and after eleven months of labor made artificial connections between the different parts of the chasm.
These vertical pits are formed by the wearing down, from the top, by the waters which become ingulfed in them. This mode of their formation was demonstrated to me in 1895, when I was in Great Britain under a commission from the French Minister of Instruction. I then explored several caves in which the rivers were still running, and satisfied myself that the pits were simply absorbing wells. Such wells are not effective now in southern France and Austria, but in northern Europe, where rain is more abundant, they are still operative. I found the plainest evidence of this fact in Yorkshire, at the Gaping Ghyll, Ingleborough, where a river precipitates itself at one leap one hundred metres under the earth. English investigators and travelers had tried without success to descend into it in 1845, 1870, and 1894, having conquered only about one hundred and ninety-five feet of its total depth of two hundred and twenty-nine feet. It took me twenty-five minutes to go down upon a rope ladder which was suspended in the midst of the cascade. Fortunately, the pit had the daylight to the very bottom—a wonderful spectacle, compensating me for all my trouble and the long douche bath which greeted me at the end of the descent, where stretched an immense Roman nave nearly five hundred feet long, eighty feet wide, and ninety feet high, without any sustaining pillar. From the middle of the roof of this colossal cavern fell the cascade in a great nimbus of vapor and light—a wonderful fantastic scene, such as Gustave Doré or Jules Verne could never have imagined. The most pleasant feature of the whole of it, however, to me was the thought that I had succeeded where the English had failed, and on their own ground. The people were nevertheless very pleasant to me, and at my instance have continued the exploration and made some new discoveries.—Translated for the Popular Science Monthly from the Revue Scientifique.
[SKETCH OF CHARLES HENRY HITCHCOCK.]
The name of Prof. Charles H. Hitchcock is closely associated with the progress of New England geology, especially with the discovery of the great terminal glacial moraine, and, in connection with the name of his father, Dr. Edward Hitchcock, with the study of the fossil bird tracks of the Connecticut River Valley.