Correspondence — Dugald Bell. 335 



explanation involves certain difficulties. The shape of the outlier, 

 as I still think it must be called, is roughly oval ; the mass dropped 

 in would therefore be cone-shaped. If it were a case of piping, 

 which I do not think it is, this might be intelligible, but it is 

 difficult to conceive a fault taking such a form. Nor is the difficulty 

 lessened by the occurrence of several other small outliers in the 

 immediate neighbourhood. 



The structure seemed to me to be the same as that of the narrow 

 strip of Tertiary beds near Lulworth, as Mr. Fisher suggests, except 

 in one detail. In both cases the chalk, after running horizontally, 

 or even dipping gently southwards, turns abruptly up so as to dip 

 at 80° or more northwards ; and in both, Tertiary beds, reposing 

 naturally upon the Chalk, have shared in the flexure, and have been 

 preserved from denudation in the elbow of the fold. But while at 

 Lulworth the Isle of Purbeck fault coincides with the abrupt upturn 

 of the strata, and thus runs between nearly horizontal Chalk and 

 Eocene and nearly vertical Chalk, at Bincombe the Ridge way fault 

 runs at the base of the Chalk, and between it and Oxford Clay. 

 I was not able to find any faulting there between the Chalk and the 

 Eocene. That the abrupt upturn traverses the Bincombe outlier, we 

 know by the fact that the gravels composing it are partly vertical, as 

 shown by Mr. Fisher, and partly gently inclined, as proved by an 

 exposure close to the western end of the outlier, where the chalk 

 clips at only 15°. I quite agree with Mr. Fisher that in passing 

 from south to north he is reading an ascending section in the 

 Eocene strata. A. Steahan. 



Cardiff, 8th June, 1896. 



THE AYRSHIRE "SHELL-BEDS." 



Sir, — Many of your readers have doubtless been interested by 

 Mr. John Smith's letter in your last number regarding his discovery 

 of " interglacial shell-beds " at various heights in Ayrshire. Mr. 

 Smith also read a paper on the subject at a recent meeting of the 

 Geological Society of Glasgow. 



While fully acknowledging Mr. Smith's great industry and 

 perseverance in tracing out these " shell-beds," I would ask leave 

 through your columns to repeat a caveat which I ventured to 

 express at the meeting referred to, viz., against assuming offhand 

 that the deposits are necessarily " interglacial," or true marine 

 deposits in situ. It appears to me that there are many hints and 

 indications that they may be accounted for in another way, and that 

 it will require further prolonged and careful observations before we 

 can pronounce upon them with any certainty. There can be no 

 doubt, to begin with, that the Clyde ice extended in great force over 

 the lowlands of Ayrshire up to the feet of the Galston and Muirkirk 

 Hills. Boulders of West Highland schists are found plentifully as 

 far up as the neighbourhood of Loudon Hill, and in similar localities. 

 The abundant deposits of sand, gravel, and silt in some of the side- 

 valleys are just what might be expected in these circumstances. 

 The crushed and fragmentary condition of the shells, or very many 



