168 CAVES AND CAVE DEPOSITS. 
of the upper cave, which is usually dry, as you pour water out of 
the mouth of a kettle; and well it might, for, if the swallow- 
hole that feeds it was full to overflowing, it had the pressure of 
more than eleven atmospheres upon it from that alone, to 
say nothing of some 200 feet fall from the bottom of the 
swallow-hole to the cave. 
This was one of the most instructive geological phenomena 
it has ever fallen to my lot to witness. Here I saw what was, to 
all intents and purposes, a local cataclysm. Gentle slopes of 
pasture, where usually no stream ran, were suddenly gashed by 
a torrent, and the débris swept far away across the lowlands. 
Underground passages, high above the present water-channels, 
were swept clean by the body of water forced through them 
under enormous pressure. Caves that had been sealed up for 
years with barriers of stalagmite, which one would have thought 
might have defied the rush of any flood, were burst open. Most 
of this débris—all, in fact, that was moved by the first rush of 
water—was carried down the valley. Some remained around 
the mouth, and some in embayed~-corners in the caves. Here 
we saw fragments of stalagmitic floors, mixed up with débris 
washed in from the swallow-holes above. Some might have 
seen here evidence that, after the cave had been formed and 
occupied and gently filled by earth and coated and partitioned 
by stalactite and stalagmite, there came an age of flood—perhaps 
of submergence—when the old deposits were resorted, the old 
floors broken up, and that the cave then entered upon another 
phase of its history. How different the facts! I saw this 
revolution taking place. It was all over in three short hours. 
It was another illustration of the great law of Uniformitarianism, 
which I have heard the Duke of Argyll well state thus: Zoca/ 
catastrophic action is not inconsistent with continuity of causation. 
We must bear these things in mind when we are examining 
cave-deposits. 
The peat torn away from the mountain-side above was so 
beaten up in this great natural churn that the water of the tarn 
did not get clear for months. The sediment did not settle for 
three weeks in a long glass which I filled during the flood, 
There must have been a layer of fine carbonaceous clay formed 
over the bottom of the tarn and in many a deep cave-pool after 
that storm. When the rain ceased, the water soon ran off the 
mountain-side, and I went up to examine Gaping Gill, the 
great swallow-hole that feeds the cave. I found a passage 
opened out among some blocks on one side of the stream a 
little above the chasm. I thought I might perhaps find a zigzag 
descent, which would lead me down into Gaping Gill Hole. So 
I crept in. 
I soon got beyond the light, and therefore took the precau- 
tion of throwing stones in front of me before I advanced. I 
