234 Reports and Proceedings — Geological Society of London. 



II. —March 26, 1879.— Henry Clifton Sorby, Esq., F.R.S., Presi- 

 dent, in the Chair. The following communications were read : — 



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

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

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

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

 previous Observations." By D. Mackintosh, Esq., F.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 Sol way Firth to 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 abun- 

 dant 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 south-east 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 dis- 

 persion 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 North-west 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., F.G.S., and John Home, Esq., F.G.S. 



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

 proceeded to describe the different islands, reviewing in succession 

 the physical features, geological structure, the direction of glaciation, 

 and the various superficial deposits. From an examination of the 

 numerous striated surfaces, as well as from the distribution 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 Scallo- 

 way and Fitful Head, blocks derived from the Old Red Sandstone 

 formation on the eastern sea-board are abundant in the Boulder-clay 

 on the west side of the watershed. The relative distribution 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 period of 

 general glaciation Shetland nourished a series of local glaciers, which 

 radiated from the high grounds, the direction of the striae being at 

 variance with the older system, while the morainic deposits also differ 

 in character from the Boulder-clay produced by the great Mer de 

 Glace. The authors described the order of succession in the Old Red 

 Sandstone formation in Shetland, and referred to the discovery of an 

 abundant series of plant-remains in rocks which have hitherto been 



