Reports and Proceedings — Geological Society of London. 235' 



• — 

 Geological Society of London. 



L— February 21st, 1900.— J. J. H. Teall, Esq., M.A., F.K.S., 

 President, ia the Chair. The following communications were 

 read : — 



1. " The Bunter Pebble-Beds of the Midlands and the Source of 

 their Materials." By Professor T. G. Bonney, D.Sc, LL.D., F.E.S., 

 F.G.S. 



The author states the results of occasional work in the Bunter 

 Conglomerate of Staffordshire. After a sketch of matter already 

 published, he gives additional particulars of the lithology of the 

 pebbles, more especially of the felstones and of some rather compact 

 dark rocks. Of the former he has now obtained about thirty 

 varieties : ortboclase-felsites and porpbyrites, some with, others 

 without quartz ; several contain tourmaline, which sometimes 

 has replaced biotite, sometimes felspar. One pebble exhibiting 

 reddish spherulites in a dark matrix, once doubtless glassy, but 

 now devitrified, is not like any British rock known to the author. 

 Of the dark pebbles, some are fine-grained quartzites blackened 

 with opacite ; others, varieties of ' schorl-rock ' ; and two, (which 

 Dr. G. J. Hinde has kindly examined) are radiolarian cherts, 

 which, however, cannot be more precisely identified. 



The mode of transport and source of the pebbles are next 

 considered. The reasons, already published, for a fluviatile, as 

 opposed to a marine, origin are briefly summarized. If the former 

 be accepted, certain conditions must be satisfied, which bear directly 

 on the position of the source. These beds I'epresent the destruction 

 of large masses of rock. If brought by rivers, those must have 

 been important and powerful, of a continental rather than an 

 insular type. Hence the necessary physical conditions exclude 

 limited districts near the Midlands, such as the Wrekin, Lickey, 

 Hartshill, and Charnwood, even if they included (which is not the 

 case) the right types of rock. As regards the Longmynds, their 

 argillites, if they occur, are not common ; their conglomerates da 

 not exactly resemble the Bunter pebble-beds ; their ' Torridonian ' 

 is a quartz-rhyolite rather than a quartz-felspar grit. The rocks 

 required cannot be supplied from eitber Wales, the Lake District, 

 or the Pennine range, and we have no reason to suppose them 

 concealed under Eastern and South- Eastern England. We have 

 therefore to choose between a southern and a northern source. 

 Cornwall and Devon might perhaps furnish the schorl - rocks ; 

 possibly also one or two varieties of felstone (though this is doubt- 

 ful) and the right quartzites and quartz-felspar grits occur in the 

 Budleigh Salterton pebble-bed. But the characteristic flat ellipsoidal 

 pebbles of grit, dominant here, are not found in the Midlands. 

 Physical conditions also seem opposed to a northward flow of the 

 rivers of Britain in the earlier part of the Trias. In Scotland, 

 however, we find the right varieties of quartzite, the Torridoniau 



