170 CAVES AND CAVE DEPOSITs. 
limestone, and I at once suspected the cause of the smell 
When I rubbed a handful of this sand together there was the 
same fetid smell at once produced. The air, tangled in the 
seething flood, was carried down the valley, and, when released, 
gave off the gases caught up from the pounded rock. 
As we cannot follow these watercourses down from above 
through all their subterranean wanderings, let us go down into 
the valley below where the water comes down, and see if we can 
work our way back into the hill towards the foot of the great 
chasm, and see what is going on there. It is here we find what 
is more properly a cave being formed. The water drops from 
one level to another, then runs along between the beds, and 
drops again. By putting your ear to the fissured rock in one 
place, you can hear, from the deep recesses of the earth, the 
sound of a waterfall that man has never seen. Not far off, a 
beautiful clear river flows out of the lower cave. This is 600 
feet below the swallow-hole, where the water enters on the hill 
above. When the rain floods the stream above, this, too, runs 
turbid. Some 20 feet above it is the entrance to the other cave, 
the celebrated Ingleborough Cave, a more ancient outfall for 
the water, which now runs at the lower level. 
This cave was explored many years ago by Mr. James Farrer. 
I have followed it for about a quarter of a mile, and, with some 
others, been let down to a lower level at the end. We squeezed 
our way along till we came to a long, deep cave, full of water, 
which seemed to flow gently towards the mouth of the lower 
cave In the great flood of 1872, all the subterranean caves 
and fissures were filled, and the water spouted out of the upper 
cave, carrying along with it great masses of rock, which helped 
to break up the stalagmitic floors and barriers. This flood was so 
exceptional that most of the débris was carried clean away ; but 
we saw, when we examined the ground round the mouth of 
the cave, and the well-known passages inside, what had been 
going on; how stalagmitic floors had been undermined, broken 
up, and redeposited, and how the torrent débris was sometimes 
left in the embayed corners of a limestone cave. But this was 
a cave not far above the existing watercourse. When a cave 
has been formed in the side of a rapidly-deepened gorge, where, 
however high the flood may rise, the water can never sweep it 
out with a rush, gentler processes of denudation and deposi- 
tion still goon. The débris that falls about the mouth poonds 
back the rain, and gathers in the fissured rock, and turns in the 
rivulet that would have trickled down the hill. The damp clay 
clings to the rock and frets away its surface, and things washed 
in work their way down along the face of the opening, gradually- 
weathered limestone, and lie in clay washed down with them, 
It is easy to distinguish the chemically-fretted rock from that 
which has been worn, smoothed, and rounded by the mechanical 
action of the sand and pebble-laden water, as you can distinguish 
