258 POPULAR SCIENCE MONTHLY. 



fastened at the end of it for a seat. The gouffre of Vigne Close, in 

 Ardeche, which is about six hundred feet deep, has five successive 

 pits, and its complete exploration required three days. The bottom 

 of the pit may be a simple cleft in the rock, or an immense cathedral- 

 like chamber; as at Rabanel, near Ganges, and Herault, the deepest 

 abyss in France, the vault of which expands into a gigantic nave, 

 five hundred feet high, which is lighted by the beam of light that 

 falls through the opening, presenting a grand and indescribable spec- 

 tacle. Some pits of less depth, as the Tin doul de la Vayssiere, in 

 Aveyron, and the Padirac well, in Lot, both leading to underground 

 rivers, enjoy a still more complete illumination. Considerable talus 

 banks close the ends of these broad pits, and are generally produced 

 by the caving in of the roofs of caves. 



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 hy- 

 pothesis 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 six- 

 teen 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, de- 

 stroy 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, Avey- 

 ron, is one hundred and six metres deep, and abuts upon a large sub- 

 terranean river, which supplies the Sorgues of Saint-AfTrique, 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 



