Mackintosh — Geological Notes on Devon. 297 



■within the large pot-shaped cavities. Here, as elsewhere, some of 

 the holes have been usurped by land-shells.* 



The testimony of the above P^oZas-bored, grooved, pitted, and 

 honey -combed rock-surfaces to marine denudation amounts to this : 

 they show that the sea has not only stood at various levels up to a 

 height of at least 240 feet above existing mean water-mark, but that 

 many of the larger features of land surface with which they are asso- 

 ciated have been formed by the sea. The forms of the cliffs are 

 evidently a part of the same class of effects, and are, therefore, 

 likewise of marine origin, while the preservation- of wave-marks 

 and PAoks-borings proves the extreme slowness of atmospheric action, 

 and thus furnish a negative presumption in favour of the sea, and 

 not the atmosphere, having been the primary or great denuding 

 agent. Not only are the phenomena of denudation in this district 

 clearly marine, but those of deposition or accumulation point in the 

 same direction. 



Valley of Kenfs Cavern. — The main valley, on the west side of 

 which this celebrated cavern is situated, runs S. and N. from sea to 

 sea, or from Torbay to Ansty's Cove. It is a pass open at both 

 ends, with too little inclination to give to any supposed former 

 stream a denuding power. The principal tributary valley has a 

 greater slope, but it merges into the valley which leads to Torquay. 

 No watershed sufficient to supply this valley with a brook possessed 

 of excavating power, could have existed in this district in post- 

 glacial times, or since the ground acquired its present general con- 

 tour. The first denudation of these and other valleys, is explicable 

 by branching currents having a clear thoroughfare, supplemented by 

 sea-coast action, producing cliffs. After their excavation, the valleys 

 must have been filled at least to a certain height (Mr. Pengelly 

 believes they were entirely filled up) with stony loam, which 

 was afterwards removed, with the exception of the remnants now 

 lining their sides, or covering their bottoms. The loam in Kent's 

 Cavern is similar to that covering the neighbouring ground. In 

 many parts it is full of stones, and very unlike a loess or re- 

 deposition by freshwater floods, while the idea that the sea left the 

 valley filled wdth loam up to the level of the cave, so as to furnish 

 the brook with a bed to enable it to carry the loam and stones into 

 the cave appears, to say the least of it, a forced explanation. There 



1 The late M.N. R. Bouchard, of Boulogne -sur-mer, wrote' a paper entitled 

 " Ohservations sur les Helices Saxicaves du Boulonnais," printed in Vol. xvi. of the 

 " Annales de Sciences Naturelles," in which he expresses his belief that these lime- 

 stone perforations are the work of land-snails. M. Bouchard's observations were 

 repeated and confirmed by Miss E. Hodgson, of Ul-verstone (see Geologist, Vol. vii., 

 Feb., 1864, p. 42). The late Dr. S. P. Woodward — than whom no higher authority 

 upon Mollusca can be quoted — decided against the snail-theory, and referred the 

 Ulverstone examples (presented by Miss, Hodgson, and preserved in the British 

 Museum) to the decomposition of the rock by carbonic acid dissolved in rain-water — 

 the form of the cavities often resulting from the former presence of fossils. The 

 writer has seen numerous similar examples of weathered and perforated limestone 

 rocks at Gibraltar and elsewhere. — H.W. 



2 The best preserved borings have retained the appearance of irregularly spiral 

 ridges and funows. 



