We reckoned that we had by this time travelled underground about half
a mile, and as we had been descending rapidly all the way, the
distance beneath the surface must have been considerable. My theory
with regard to this stream was that it was a tributary of the
subterranean Ouysse; but the fact that the cavern ran north-west made
me change my opinion, and conclude that this water-course took an
independent line towards the Dordogne.

A little beyond the last pool the running water suddenly vanished. We
looked around to see if it had taken any side passage; but no: it
simply disappeared into the earth, although no hole was perceptible in
its stony channel. It passed by infiltration into some lower gallery,
where the light of a candle had never shone, and is never likely to
shine. But we had not reached the end of the cavern, although the
passage became so low that we had now really to go down on all-fours
in order to proceed. We had not to keep this posture long, for again
the roof rose, although to no great height. We walked on about fifty
yards or more, and then came to the end. There was no opening anywhere
except by the way we entered. We were like flies that had crawled into
a bottle, and a very unpleasant bottle it might have proved to us. We
noticed--at first with some surprise--that, although there was not a
drop of water now in this _cul-de-sac_, our feet sank into damp sand
that had evidently been carried there by water. Sticks were also lying
about, and the walls up to the roof were covered with a muddy slime.
It was evident that this hole had been filled with water, and not very
long ago; probably the last thunderstorm accounted for the signs of
recent moisture. While we were talking about this, a strange, muffled,
moaning sound reached our ears. We looked at one another over the tops
of two candles. 'Thunder,' said my companion. In a few minutes the
same dismal moan, long drawn out, came down the cavern, which acted