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CAVES AND CAVE DEPOSITS. 169 
found the slope increasing rapidly, and then all of a sudden the 
stones dropped into a deep hole, down which they whirred, 
knocking the sides here and there till they dropped, with a 
booming noise, into deep water below. I wriggled out, and 
returned another day, with friends and candles and string, for I 
could not drop the stones straight so as to clear the sides, and 
so estimate the depth by the time they took in falling. Some- 
times 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 io jydge 
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 convenient weight, and I found that the 
water here plunged into a vertical hole 360 feet from the grass- 
covered turf above. 
This was not, however, the principal chasm, and I 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, andso 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 water-courses 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 acidu- 
lated water running off the peaty moor, and opening out the 
crevices in the jointed limestone. 
Then, there was the mechanical action observed on a grand 
scale in storm—the boulders and pebbles pounding away the 
solid rock. And next, there was 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 
