This effect of gloom, horror and sublimity is the result of geological conditions and the action of water, which together have produced many similar phenomena in the region of the causses, but in no other case, I believe, with such power in composing the picturesque.  Imagine an open plain which in the truly Dark Ages whereof man has had no experience, but of whose convulsions he has learnt to read a little from the book whose leaves are the rocks, cracked along a part of its surface as a drying ball of clay might do, the fissure finishing abruptly and where it is deepest in front of a mass of rock that refused to split.  This was apparently the beginning of the Gouffre de Revaillon.  Then came another submersion which greatly modified the appearance of things.  There was evidently a deluge here after the land had dried and cracked, and it must have lasted a very long time for the waves to have hollowed, smoothed and polished the rocks inside the caverns and elsewhere as we now see them.  Those who have observed with a little attention a rugged coast will, without being geologists, recognise the distinctly marine character of the greater number of these orifices in the calcareous district of the causses.  The washing and smoothing action of the sea along the sides of the gorges which cut up the surface of the country in such an astonishing manner is not so easy to distinguish.  But the reason is obvious.  This limestone rock is by its nature disintegrating wherever it is exposed to the air and frost, and the foundations of the bastions which support the causses are being continually sapped by water which carries away the lime in solution and deposits a part of it elsewhere in the form of stalactite and stalagmite in the deep galleries where subterranean rivers often run, and which probably descend to the lowest part of the formation.  Thus by the dislodgment of huge masses of rock which have rolled down from their original positions, and the breaking away of the surfaces of others, the most convincing traces of the sea’s action here have nearly disappeared.  In the gorge of the Alzou, however, near Roc-Amadour, about 100 feet above the channel of the stream, there is a considerable reach of hard rock approaching marble, the polished and undulating surface of which tells the story of the ocean, just as the sides of the caverns in much more elevated positions tell it.

In the rock where the fissure ends at Revaillon is an opening like a vast yawning mouth, the roof of which forms an almost perfect dome.  Adown this a stream trickles towards the end of summer, but plunges madly and with a frightful roar in winter and spring.  The steep sides of the narrow ravine are densely wooded, and the light is very dim at the bottom when the sun is not overhead.  I made my first attempt to descend the dark passage in the early summer, but there was too much water, and I was soon obliged to retreat.  One afternoon in October I returned with a companion,