ON CAVES. 87 
falling. Sometimes the weight I attached to the string was 
too small, so that the increased weight of the string itself, when 
wetted by the splash of underground waters, prevented my 
being able to judge whether my plummet had touched the 
surface of the water below or not. Sometimes the jagged 
rocks cut my string, and I lost hundreds of feet in this way. 
At last, however, I got the right sort of string and a con- 
venient weight, and | found that the water here plunged inio 
a vertical hole 560 feet from the grass-covered turf above. 
This was not, however, the principal chasm, and 1 saw a 
curious sight on the southern, or lowest, face of the great 
chasm beyond: it was battered and bruised as if it had been 
bombarded for hours, and so it had. In that flood hundreds 
of boulders, carried forward by the rush of water, were hurled 
against the opposite face of rock, and then, dropping into 
the great chasm, were hurried away through the subterranean 
watercourses and caves down to the valley far below, where 
they still rolled on with a noise like thunder over the smooth, 
rocky bed of the stream, till arrested when the velocity of 
the water was checked in the wider spaces, or finally stopped 
in the little tarn below. 
Here was the whole story of the formation and infilling of 
limestone caves, and the sudden breaking up of all the older 
deposits and the return of tranquil deposition, to be read in 
Nature’s clearest writing. 
First we saw the results of the chemical action of the 
acidulated water running off the peaty moor, and opening out 
the crevices in the jointed limestone. 
Then there was the mechanical aetion observed on a grand 
scale in storm,—the boulders and pebbles pounding away the 
solid rock. And next there were the sand and mud left as 
the water subsided, and the old state of things returned. 
Another curious fact I noticed, which shows how the frag- 
mentary rock is rubbed down into mud by the action of 
running water. There was a fetid smell arising from this 
flood water, such as the people about there said they had not 
perceived before. I followed up the stream, and noticed a 
great quantity of black sand thrown down here and there 
along its course. This was derived from the bituminous 
limestones of the lower part of the Yoredale rocks and the 
upper part of the mountain 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 roek. 
H 2 
