ON CAVES. 11 



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 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, 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 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 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. 



