[ 367 ] 



LIX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 295.] 



March 26, 1879.— Henry Clifton Sorby, Esq., E.R.S., President, in 



the Chair. 



rpHE following communications were read : — 

 -*■ 1. " Results of a Systematic Survey (in 1878) of the Directions 

 and Limits of Dispersion, Mode of Occurrence, and Relation to 

 Drift-deposits of the Erratic Blocks or Boulders of the "West of 

 England and East of Wales, including a Revision of many years' 

 previous Observations." By D. Mackintosh, Esq., E.G.S. 



The author's researches lead him to the following conclusions : — 

 Boulders from the North-Criffell range and Lake-district can be 

 traced from the Solway Eirthto near Bromsgrove (about 200 miles), 

 and over an area in greatest breadth (from near Macclesfield to 

 Beaumaris) of 90 miles, those from Criffell being particularly 

 abundant near Wolverhampton. Boulders from the Arenig occupy 

 a triangular area limited by a line drawn northward from Chirk to 

 the Dee estuary, and to the S.E. of that town are found as far as 

 Birmingham and Bromsgrove. The dispersion of the more distant 

 Criffell Boulders would require submergences of from 400 to 1400 

 feet ; of the Lake -district a little deeper ; while the distant dispersion 

 of the Arenig Boulders took place at submergences between 800 

 and 2000 feet. The author describes several of the more local 

 drifts, and correlates the Lower Boulder-clay of the N.W. with the 

 Chalky Boulder-clay of the east of England. He considers floating 

 ice, not land-ice, to have been the agent of dispersion. 



2. " On the Glaciation of the Shetland Isles." By B. N. Peach, 

 Esq., E.G.S., and John Home, Esq., E.G.S. 



After an account of previous opinion on the subject, the authors 

 proceeded to describe the different islands, reviewing in succes- 

 sion the physical features, geological structure, the direction of 

 glaciation, and the various superficial deposits. Erom an exami- 

 nation of the numerous striated surfaces, as well as from the dis- 

 tribution of Boulder-clay and the dispersal of stones in that deposit, 

 they inferred that during the period of extreme cold Shetland must 

 have been glaciated by the Scandinavian Mer de Glace, crossing the 

 islands from the North Sea towards the Atlantic. In the island of 

 Unst, blocks of serpentine and gabbro are found in the Boulder-clay 

 on the western shores derived from the rock-masses occurring on the 

 east side of the watershed. Moreover, on the mainland between 

 Scalloway and Eitful Head, blocks derived from the Old-Red-Sand- 

 stone formation on the eastern sea-board are abundant in the 

 Boulder-clay on the west side of the watershed. The relative dis- 

 tribution of these stones in the sections on the west coast is in direct 

 proportion to the relative areas occupied by the rocks on the east 

 side of the watershed. It was likewise pointed out that after the 



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