318 Prof. Nicholson — Valleys of Erosion. 



Of those who assign to the burrows an organic origin, some 

 attribute them to the work of Pholades, others of Helices. I have 

 endeavoured in these communications ^ to shew that the form, direc- 

 tion, and position of the burrows, not only do not correspond 

 with those of Pholades, but also are such that it is impossible that 

 these molluscs could have excavated them ; and, further, that the 

 presence of these burrows almost at the bottom of such well-marked 

 valleys of river erosion as Miller's Dale and Tideswell Dale, is quite 

 irreconcilable with any ' marine ' theory. They must, therefore, be 

 the work of some terrestrial animal. I have found snail-shells 

 abundant in their immediate neighbourhood, dead shells in evidently 

 disused burrows, and living snails in those which presented the 

 freshest and most unweathered surfaces. 



It seems, therefore, only a fair inference to consider these the 

 work of Helices, and as such they have an interest rather for the 

 zoologist than the geologist. 



On former occasions I have been led to connect Helix adspersa 

 chiefly with the burrows ; but on this I noticed that the burrows as 

 a rule were of rather less diameter than the majority of those at 

 Llandudno and on the hill behind Matlock, and that Helix nemoralis^ 

 (and sometimes H. lapicida ^) was the usual occupant. 



Now that attention has been drawn to them, they will probably 

 be found abundantly, and it may be possible to discover by further 

 observation the precise mode of excavation, whether by mere friction, 

 by an acid secretion, or by both agencies ; * as well as the purpose for 

 which they are made. If it be for hybernation, it is strange that the 

 animals should take this trouble, when . there ai-e often cracks and 

 recesses near, with which, had the rock not been limestone, they 

 would have remained content. 



VI. —Notes on some Valleys of Erosion. 



By H. Alleyne Nicholson, M.D., D. Sc, P.R.S.E., 



Professor of Natural History and Botany in University College, Toronto. ^ 



DUKINGr the summer of last year I had the opportunity of 

 visiting various localities in the State of New York which are 

 of great geological interest ; and I was particularly struck by the 

 numbers of A'^alleys which are exclusively the work of the rivers by 



quite the right kind of rock, and only found two or three burrows — and these in a 

 boulder — that satisfied me. It will not, however, surprise me if they are found 

 there ; for I had other matters in hand, and was too hurried to look carefully for them. 

 Mr. Main, Lecturer in Chemistry at St. John's College, Cambridge, has kindly 

 analyzed for me a fragment of the limestone from Derbyshire. He finds only 3'5 

 per cent of foreign matter, the rest, 96-5, being carbonate of lime. 



1 Geol. Mag. Vol. VI., p. 483 ; VII., pp. 93, 267. 



' The same species is described as tenanting burrows, especially in winter, by Mr. 

 Hodgson, Jameson's Eclin. Journal, 1846, p. 396. 



3 LinuEeus gave this name, I find, from a belief that it bored limestones. Mr. N. 

 Goodman informs me that the burrows at Monte Pellegrino are made by a fourth 

 species of Helix. 



* See for a fuller discussion of this a paper by Mr. Eofc, Geol. Mag. Vol, VII., p. 4. 



* Eead before the Eoyal Physical Society, Edinburgh, April 24th, 1872. 



