L. C. Miall — Formation of Swallow-holes. 619 



limestone, we have a suggestion of deep sea deposition, as well as an 

 explanation of the constant association with the lower sear limestone 

 of cavities of subsidence. 



We are not without direct evidence to show the possibility of the 

 sudden formation of a pit by the fall of ground which had been 

 undermined by water. About a mile to the north of Eipon, near the 

 river Ure, are a number of pits or hollows, fifty to a hundred feet in 

 diameter, and in some cases as much as seventy feet deep. They 

 are commonly of conical shape, some are perpendicular shafts. The 

 majority are sunk through the New Eed Sandstone, which here over- 

 lies beds of Eed Marl, gypsum, and Magnesian limestone. In a 

 paper read before the West Eiding Geological Society, the Eev. J. 

 S. Tute has placed upon record several accounts given by eye- 

 witnesses of the sudden production of these pits. In 1860 the Eev. 

 F. H. Dunwell observed the falling in of a pit 69ft. deep and 22ft. 

 wide. Twenty years ago one fell in at Sharrow during the night. 

 Forty years ago a stack upon which some men were working, near 

 Bishop Monkton, disappeared, and its place was occupied by a hole 

 which still remains. These pits are undoubtedly due to the yielding 

 of the ground above a large hollow or cavern, but the difficulties of 

 observation are so great as to prevent a full comprehension of the 

 circumstances of excavation. Mr. Tute is of opinion that the sub- 

 terranean waste has gone on in the Eed Marl and gypsum beds. I 

 should myself incline to believe that caverns in the Magnesian lime- 

 stone have undermined the ground. 



In many parts of Craven, particularly in Chapel-le-Dale and 

 Eibblesdale, there are stories of chasms suddenly formed, but I have 

 as yet been unable to authenticate any of these accounts by the 

 testimony of eye-witnesses. If attention is once called to the point, 

 well-attested cases will quickly accumulate. (See note ante p. 518.) 



It is easy to understand that swallow-holes formed by subsidence 

 may be much disguised by the superficial character of the ground. 

 Some of the large conical depressions without an outlet, which occur 

 in a calcareous district, may be due to the yielding of undermined 

 rock beneath a thick mass of drift. I am inclined to adopt this 

 explanation of many basins which occur in the Glacial drift of 

 Craven, especially with regard to such as are pervious to water. 

 Some of the most remarkable of these occur near Kirby Lonsdale, 

 at the entrance to Underley Park. I do not know that Mountain 

 limestone underlies them, though it is plentiful close at hand, for 

 the thick superficial deposits and the large faults which disturb the 

 district render it unsafe to infer that such i^ the case. But the 

 supposition is not improbable,^ and if it should be confirmed, we 

 may find in the hypothesis of concealed swallow-holes a less ad- 

 venturous explanation of these singular excavations than one which 

 has gained currency, viz., that large blocks of ice have been heaped 

 round with drift, and afterwards melted. Around Ingleborough, and 



1 In the subsequent discussion, Mr. T. McK. Hughes, of the Geological Survey, 

 gave his opinion that the strata beneath these hollows were Devonian and non- 

 calcareous. He also supported the ice theory mentioned in the paper. 



