T. G. Bonney — On Supposed Pholas Burrows. 269 



In many places the rock is clearly scarped, but in this it is 

 rather more weather-worn than elsewhere. Of course if this cliff 

 has been formed by the erosive action of pick and crowbar, there 

 is an end of the Pholas theory. 



(2.) But even waiving this objection, and supposing the rock-face, 

 like many others in the valley, to be one due to natural forces, is it 

 likely that burrows of Pholades should exist in such a situation ? 

 The gorge, as I have said, is one, if ever I saw an example, of 

 subaerial fluviatile erosion. The holes are not a dozen feet above 

 the present level of the stream. If, then, the existing Millers Dale 

 had ever been a land-locked fjord, might we not expect to discover 

 some traces of the deposition which must then have been going on 

 from lateral streams ? I could not see a trace of a terrace of river 

 drift, and so convinced am I that the greater part (if not the whole) 

 of the gorge has been cut out by stream, rain, and frost, since Derby- 

 shire had its last sea bath, that I should as soon expect to find a 

 whale's skeleton in the Combe de Queyraz, or any other Alpine glen, 

 as a Pholas burrow at the bottom of Millers Dale. 



Next day, while descending Salter's Lane, towards Matlock 

 Bridge, I observed on the pastures on either side of the road a 

 number of large blocks of limestone, many of them from ten to 

 twenty cubic feet in contents, which no doubt mark the outcrop of a 

 bed differing somewhat in mineral character from those above and 

 below. They form an irregular band on the hill side, between the 

 upper and lower sheets of toadstone, very near to the letter S on the 

 Geological Survey Map, The limestone, though compact internally, 

 has a soft chalky appearance externally, and I felt convinced, from 

 its general appearance, that here, if anywhere, I should find burrows. 

 It needed little search to discover them, for they were abundant on 

 either side of the road. Here again, although they were not re- 

 stricted to any one face of the rocks, the burrowing animals appeared 

 generally to have selected some existing crack, depression, or under- 

 side of a projection, as a lodgement in commencing their task. As 

 at Llandudno, very many were quite near to the ground, and not a 

 few were only channels, without any signs of having ever been 

 more deeply burrowed. Most of them were directed vertically up- 

 wards, but there was just the same irregularity in direction and in 

 section that I have already noticed. One specimen, which now lies 

 before me, contains about fourteen or fifteen of these burrows, varying 

 in depth from barely half an inch to nearly two and a-half inches, 

 most of which are driven upwards ; but so intricate are they, and so 

 honeycombed are some parts of the rock, that no description, and 

 not even a drawing, could give a true notion of their arrangement. 

 In several cases one burrow has encroached on the party wall 

 which separated it from another, so that the two are either thrown 

 into one for some distance, or else joined by a small circular aper- 

 ture. I did not find any helices in those that I probed ; this, how- 

 ever, may be due to the season of the year ; but after examining 

 these instances my conviction is stronger than ever that no animal 

 of the Pholas form could have produced such excavations, while a 



VOL. VII. — NO. LXXII. 18 



