RAMSAW DRIFT AND GLACIERS OF N. V ALES. 373 



the sea. Its dimensions are 9 yards by 5, by 2 yards in height. Its 

 weight cannot be less than from 90 to 100 tons. The parent rock, 

 of felspar-porphyry, is at least a mile distant. 



I am well aware that heretofore it has not been customary to con- 

 sider accumulations at so great an elevation as belonging to glacial 

 marine deposits. They have either been altogether disregarded, or con- 

 founded with glacier-moraines . But when we consider their continuity 

 with the shell-bearing strata, their regular smoothly sloping outline, and 

 their gradual change from gravelly drift with a few scattered boulders 

 on the coast, to the coarser and more massive accumulations among 

 the mountains ; and further, if we add to this the travelled boulders 

 and masses of rock on the summits of hills and ridges 2300 feet high, 

 it seems to me impossible to resist the conclusion, that the whole 

 material from the present sea-margin upwards is of marine origin, 

 and due to the operation of one general set of causes extending over 

 a definite period. 



In this communication I will not enter on the general proofs of the 

 ancient extension of glaciers among these mountains, formerly so 

 beautifully inferred by Dr. Buckland*. From numerous observa- 

 tions I have convinced myself, on what I consider perfect evidence, 

 that this inference is correct, and with the materials I have collected 

 I may at some future period produce a map of the extent and course 

 of the glaciers of Caernarvonshire, or of North Wales generally. 

 Believing then in their former existence, it is sufficient for my present 

 argument to state that belief. 



The " drift" deposits, above mentioned, often rest on and sometimes 

 conceal the rounded, polished, grooved, and scratched surfaces {roches 

 moutonees), due to the operation of glaciers, the effects of which are 

 so clearly traceable in the Pass of Llanberis, Nant Francon, and other 

 valleys of Caernarvonshire. Roches moutonees, surrounded by, and 

 partly denuded of drift, may be seen near Llyn-y-Gader, in the 

 neighbourhood of the Caernarvon and Beddgelert road, and in the 

 valley leading from the base of Snowdon to Capel Curig. These great 

 glaciers, therefore, preceded the deposition of the " drift," — a circum- 

 stance mentioned by Dr. Buckland, in 1841 f, who however attri- 

 butes its distribution " to a great diluvial wave or marine current, 

 advancing from the north, and propelling before it the materials of 

 which the drift is composed ;}:." It may be objected that denudations 

 during the submergence of the country must have removed the glacier- 

 markings. On the other hand it may be replied, 1st, that the ex- 

 posed polished rocks are for the most part of extreme hardness ; 

 2nd, that rocks rounded and polished by glaciers, in offering surfaces 

 of small resistance to the sea-waves, run a high chance of escaping 

 their wasting influence during submergence ; and 3rd, that they prin- 

 cipally occur in the recesses of valleys that anciently, at various 

 levels, formed narrow sinuous arms of the sea, where on the whole 

 still water would prevail. The superincumbent drift has in a great 

 measure preserved them from the wasting effects of atmospheric in- 

 fluences in more recent times. 



* Loc. cit. t Gcol. Proc. vol. iii. p. 579. % Loc. cit. p. 584. 



