Rev. T. O. Bonney — Burrows in Limestone Rock. 485 



(&). By being dropped from floating or stranded bergs. The 

 objection to this is the difficulty of understanding, without assuming 

 a considerable alteration of level, whence these blocks could have 

 been derived, and the evidence (as it appears to me) in the contour 

 of parts of the Great, and more especially of the Little Ormeshead, 

 of glacial subsequent to marine action. 



(c). By being moved to their present position by land ice. The 

 difficulty in this explanation is that the only broken crest of rock 

 now visible (to the N.W.), from which such a boulder is likely 

 to have been derived, is but little higher than it. This crest, 

 however, is higher than the base of the boulder, and the rock to the 

 S. is still more elevated, although it is now a bare scar. Possibly 

 some of these blocks may represent a former extension of the ' reef ' 

 over this now denuded portion. There is also much higher ground 

 to the S.E. Mr. Darbishire appears to feel a difficulty in regarding 

 a block as ' perched,' unless it has travelled from a distance, in 

 saying, " They are uniformly of a stone apparently identical with 

 the beds in their immediate neighbourhood, and may often be 

 connected with a neighbouring reef of rock, both by the character 

 of the stone, and the style of wearing. A few may be found 

 actually in situ, as isolated pillars or tables," etc. (p. 14.) I never 

 supposed that they had travelled more than a few hundred yards, at 

 the most ; and the distance a block is conveyed by a glacier, will be 

 little, or great, according to the size and form of the ice- stream ; 

 nor did I intend to imply that I considered the Ormeshead glaciers 

 to be large. All the indications of an extensive glacier system are 

 wanting. Therefore, notwithstanding some difficulties, I still adhere 

 to my opinion that many of these scattered masses of limestone 

 rock are true hlocs perchees. 



(2). If, however, Mr. Darbishire is right in attributing the 

 peculiar pits and depressions in the limestone rock to the excavating 

 . action of some species of Pholas, the question is pretty well settled ; 

 for although under certain circumstances the sea (as may be ob- 

 served on many parts of the west coast of Norway) has surprisingly 

 little effect in obliterating the traces of glacial action, it is impro- 

 bable, to say the least, that any would have survived in a rock so 

 liable to denudation as carboniferous limestone, and in a position 

 so exposed as the Ormesheads. But are these pits Pholas burrows ? 



quarter wide, indicated in the middle of the side towards the spectator, in the plate. 

 At a depth of about three inches it appeared to be choked with angular fragments of 

 limestone, among which could be seen a shell, which, when uncovered a little, 

 proved to be BmciuHm undaUmi, wedged in with its spire downwards. As it had 

 a very ancient appearance, I supposed that this would make for the marine theory ; 

 but a little poking at it with a chisel showed that the fragment in contact with it 

 above was bone, probably of a sheep. Beneath the JBiwchutm, was a shell of Helix 

 aspersa. Further examination of the crack showed that it extended to the upper 

 part of the stone, and widened in that direction, so as to be at last three or four inches 

 across. It was filled with limestone fragments to within a foot or so of the top ; on 

 removing the topmost of these, 1 found a fresh bone (part of the clavicle (?) of a 

 lamb). I suspect, therefore, that the Buccinum, with the bones, were dropped 

 down the crack by a raven or a gull. I wixs confirmed in this view by finding that I 

 could not succeed in extracting them from the crack by the lateral apertui-e. 



