﻿Vol. 64.] HIGH-LEVEL PLATFOEMS OF BODMIN MOOE. 399 



them. These deposits were apparently produced by a type of 

 denudation ancient and now extinct ; they were preserved in conse- 

 quence of past climatal changes ; and the conditions which permitted 

 of their successful working were only to be understood as the 

 outcome of advanced physiographic research. 



M. M. Alloege remarked that there was a striking parallelism 

 between the past geological history of Cornwall and that of Northern 

 Britanny. Taking into account the morphological features of the 

 two areas, he thought that there was some evidence that the lower 

 platform, a little above 300 feet, — if not actually a sea-beach caused 

 by marine abrasion, — had at least been temporarily covered by the 

 Pliocene Sea, and sprinkled with marine sands at that period. 

 With regard to the two higher platforms, he saw no positive 

 evidence of marine encroachment during Tertiary time — there 

 being no traces of old sea-cliffs and no remains of shore -con- 

 glomerates. It was therefore simpler to attribute the formation of 

 the upper platforms to slow subaerial levelling and to the backward 

 working of ruissellements during the Tertiary. Such a view 

 would avoid the necessity of the intervention of a complicated series 

 of oscillations of the sea-level. A single vertical oscillation of some 

 300 feet would in this case have taken place since the Pliocene 

 Epoch, and could be accounted for by simple posthumous movements 

 along the Armorican lines of weakness. 



In regard to Glacial action, he had been struck by the very slight 

 evidence for it in .Cornwall and its great importance, on the other 

 hand, in South Wales, where its strong influence was traced in 

 the features of the scenery. He would like to know whether the 

 Author could suggest any explanation of the difference of morphology 

 of two districts otherwise so closely related. ' He welcomed the 

 appearance of the paper, as an interesting contribution to the eluci- 

 dation of the morphological features of South- Western Britain. 



Mr. G. W. Young thought that the Author's suggestion, that the 

 preservation of the beds of non-coherent wolfram-containing detritus 

 was due to the former existence of a snowfield, presented con- 

 siderable difficulties. If their preservation was due to that cause 

 alone, had not sufficient time elapsed since the passing-away of 

 those Glacial conditions to allow of their removal by denudation ? 

 As the deposits in question had already been turned over and re- 

 arranged by man in his search for tin, could any reliance be placed 

 on their present appearance? With regard to the theory that the 

 large masses had slid down to their present position over frozen 

 surfaces, he thought that the ordinary gravitational creep of such 

 masses from higher to lower ground would be a sufficient cause. 



Dr. A. Steahan remarked that the ore-deposits described by the 

 Author corresponded in their character and origin with certain accu- 

 mulations of galena which had been worked with much profit in North 

 Wales. The ore there occurred as loose lumps distributed along 

 the outcrops of lodes, and was known to the miners as ' gravel-ore ' 

 or 'round ore.' There was a suggestion in Cornwall of Glacial con- 

 ditions having supervened after the distribution of the ore-deposits ; 



Q. J. G. S. No. 255. 2 d 



