ON CAVES. 13 



mechanical action of the sand and pebble-laden water; as 

 you can distinguish the pholas-bored rock from that in which 

 the holes are due to weathering. On the chemically- weathered 

 surface the less soluble grains and bands stand out. This is 

 a useful test. 



When any partly-closed cave is invaded by periodic rushes 

 of rain-water, the debris is carried down from above through 

 fissures, or washed in from the mouth, and so we find re-sorted 

 drift and the material of the rainwash from the surface-soil 

 outside the cave occurring also in layers in the cave ; and if 

 the cave happens to be occupied by wild animals when not 

 flooded, we find their bones and the remains of their food 

 scattered over the floor or buried in the rainwash. 



But when the turbid water fills a pool in the cave or 

 a pond outside it, and the mud is allowed to settle down 

 quietly, the coarser falls first and the finest last. Then the 

 water evaporates or soaks through the sides, or perhaps 

 remains clear and tranquil till the next rain carries in a flood 

 of muddy water. The deposit so formed will have a tendency 

 to split along the layers of coarser sand or loam which first 

 settled down after flood that is, it would be a laminated clay. 

 As long as the pool was about the same depth, and the amount 

 of mud carried in suspension in the water was the same, the 

 thickness of the laminae would be practically the same, 

 representing just the mud in one pondful of turbid water, 

 whatever the interval between the refilling of the pond might 

 be. The turbid water may come from the bottom of a glacier, 

 or from melting snow, or from a heavy rainfall ; but it cer- 

 tainly has no necessary connection with glacial action. We 

 see laminated clay so formed commonly in the corner of any 

 old quarry, in ditches, or in caves. 



In Chapel le Dale, a valley on the west side of Ingle- 

 borough, there is a beautiful chasm which has been so opened 

 out by the action of the torrent, that you can get down to the 

 bottom, where the water plunges on to a bed of broken rock 

 and pebbles, through which it passes, as through a sieve or 

 very coarse filter, into the water-courses that carry it off 

 down Chapel le Dale. This great chasm is probably a fair 

 representative of all the large swallow-holes. Hull Pot and 

 Hunt Pot, on the flanks of Whernside, are of the same kind. 

 Probably there is in Gaping Gill somewhere a place where the 

 water in ordinary weather filters through coarse gravel, for I 

 have sent down many boards with a notice on each that I 

 would reward any person who brought it back to me, but I 

 have never heard of one of my notices being found. Yet at 

 times great boulders do get through, so it may be that the 



