398 Geological Society : — 



increasing metamorphisin, though possibly more gradual, where 

 that granite now occurs, would have been equally apparent.' 

 Evidence of metamorphism when the rocks are traced across their 

 strike is also adduced. 



Although the author does not go very fully into the question of 

 the causes of the progressive metamorphism exhibited in tracing 

 these rocks towards and into the Central Highland schists, he had 

 reason to suspect that ' the intense regional type of metamorphism 

 was linked with the same phenomena that afterwards resulted in 

 the irruption of the granite-masses.' 



June 7th.— W. Wbitaker, B.A., F.B.S., President,' 

 in the Chair. 



Mr. E. A. Bather, in exhibiting, on behalf of Mr. R. D. 

 Darbishire, a pebble found in gravel near St. Margaret's, Bowdon 

 (Cheshire), said that it consisted of liver-coloured quartzite and no 

 doubt once formed part of the Bunter Pebble-beds, though these do 

 not occur in the immediate neighbourhood of Bowdon. It had 

 been reported to Mr. Darbishire as found in river-gravel ; but 

 reference to Sheet 80 N.E. of the Geological Survey map (1-inch, 

 Drift) showed that the deposit was Drift of alleged glacial origin. 

 The specimen was an exceedingly perfect and characteristic example 

 of the pyramid-pebbles or ' Dreikanter,' such as are found in the 

 'Diluvium' of the North German plain, and in other parts of 

 the world from the Cambrian to rocks now forming, but hitherto 

 not recorded from England. These havo been explained as due to : 

 (1) human agency, (ti) glacial action (Theile), (3) compression in a 

 pebble-bed (' Packungstheorie ' of Bereudt), and (4) action of wind 

 and sand. The last explanation was the only one that met the facts 

 of the case, as proved by A. von Mickwitz (Mem. Soc. Imp. Mineral. 

 St. Pefcersb. ser. 2, vol. xxii. pp. 82-98, pis. viii. & ix., 1887). 



In illustration of his remarks, Mr. Bather exhibited a series 

 of specimens which had been collected under the guidance of 

 M. Mickwitz from the locality described by that author (shore 

 of the Obersee, south of Reval, Esthonia). They confirmed the 

 statement that the three sides of the pyramids lay at right angles 

 to the directions of the prevailing winds of the district ; they 

 showed stages between stones eroded on one face, or on two faces, 

 and the typical ' Dreikanter ' ; they illustrated the polishing action 

 of the agent on hard, fine-grained material, its differentiating 

 action on coarse-grained ; they retained the original water-worn 

 surface and shape on the under side, and a growth of lichen on 

 such small portions of the upper surface as had been sheltered 

 from the wind. Applying this explanation to Mr. Da.rbishire's 

 specimen, there still remained an unsolved problem : Was the 

 pebble eroded before or during the deposition of the Bunter 

 stratum, or at some time before, during, or subsequent to the 

 transport and deposition of the Drift? The mode of occurrence 

 of the North German specimens shows that they were eroded after 

 the deposition of the beds at the top of which they now lie ; and, 

 in the absence of contrary evidence, the same answer must be 

 given provisionally to the preceding questions. 



