450 Trof. E. Hull — Glacial Deposits of AherdeensMre. 



IV. — The Glacial Deposits of Aberdeenshire. 

 By Prof. Edwakd Hull, M.A., LL.D., F.E.S. 



MR. DUGALD BELL, F.G.S., has been so good as to send me 

 a copy of his paper on the " Shelly Clays and Gravels of 

 Aberdeenshire,"^ on which I beg leave to offer a fev7 observations, 

 as it deals with a subject in which I take much interest, namel}', 

 the *rigin and mode of formation of such deposits. His paper is 

 mainly based upon one by Mr. T. F. Jamieson, of Ellon, also 

 published in the same journal,^ and on a recent memoir by the 

 Geological Survey of Scotland.^ There is no difference amongst 

 these authors of any importance as regards the structure and com- 

 position of these post-Tertiary deposits, which are found adjoining 

 the coast of Aberdeenshire ; and they may be briefly described as 

 follows, in descending order*: — 



1. Upper Eed Clay with boulders, and a few marine forms, 

 1 to lo ft. 



2. Gravel and Sand with waterworn pebbles and shells, 40 to 60 ft. 



3. Lower Boulder-clay ("Grey rubbish"), 5 to 10ft. 



As regards No. 3, there is no difference of opinion. All are agreed 

 that it is the product of the great ice-sheet — the moraine profonde — 

 of the epoch of intensest glaciation. It is when we come to deal 

 with Nos. 2 and 1 in the above series, that we find divergence of 

 opinion amongst the authorities quoted. Thus, Mr. Jamieson con- 

 siders the gravel and sand (No. 2) to be a sort of "moraine," though 

 in some way not clearly explained, " washed " or reconstructed under 

 water, owing to which the pebbles have lost their glaciated sur- 

 faces ; in fact, the pebbles are remarkable for the absence of glacial 

 striae, which one would have supposed was strongly indicative of 

 aqueous action. The bedding is generally rude and irregular, but 

 current-bedding occurs occasionally, and the marine shells are 

 almost always fragmental. Notwithstanding all these indications 

 of deposition under water, Mr. Jamieson does not consider that the 

 beds indicate submergence. Mr. Bell concurs, and regards the 

 No. 2 series as the product of land glaciation only (p. 475). On 

 the other hand, the writer of the Survey Memoir considers this 

 deposit as " evidence of inter-Glacial submergence." 



I may here pause to enquire in the first place why, if No. 2 

 deposit has an identical, or similar, origin with No. 3 (the Lower 

 Boulder-clay), there should be so marked a distinction between 

 them ? It certainly requires some very clear demonstration to induce 

 one to believe that one ice-sheet will give rise to a stiff unstratified 

 clay with glaciated stones and boulders ; and another, to a rudely 

 stratified gravel and sand in which the pebbles are subangular or 

 rounded and destitute of glacial striee. Even Mr. Jamieson sees the 



^ Quart. Journ. Geol. Soc, Aug. 1895. 



* Ibid., vol. xxxviii. 



3 This I regret to say I have not seen ; but rely upon Mr. Bell's quotations there- 

 from, which I doubt not are correct. 



* Very clearly represented in Mr, Jamieson's Coast-section, ibid. p. 151. 



