Vol. 59.] SOUTH DEVON AND THE MIDLANDS. 331 



concerned, by the fact that in the same direction they become larger 

 and more angular ; and if we take, as a working hypothesis, the 

 deposit of the Bunter in a lake-basin or area of depression, the con- 

 ditions prevailing in the north-western area are easily explained. 



The late G. H. Morton showed that the Bunter in the Liverpool 

 district has a total thickness of 1950 feet, but of this 400 feet is a 

 sandstone in which quartz-pebbles are dispersed, and 600 feet 

 is a true pebble-bed. In this, however, the pebbles are principally 

 white vein-quartz, quartzite, and a few other rocks. Very few are 

 6 inches in diameter, and they are perfect]y smooth and ' must have 

 come from a great distance.' l That is exactly what would happen 

 in the deepest part of a depression such as has been indicated, if it 

 were the farthest from the source of supply of materials. Finer 

 material would tend to accumulate there ; the pebbles would be 

 smaller and more rounded, and by selective action those composed 

 of quartz would predominate, on account not only of the hardness 

 of the rock, but also its tendency to wear to a more rounded form, 

 and so either to survive longer, or to travel farther than rocks of a 

 less compact and amorphous structure. 



The same conditions are observed, to a considerable extent, in 

 South Devon. At Burlescombe the pebble-bed passes" into or is 

 succeeded by a deposit of small quartz-pebbles with grit-pebbles, 

 and the pebbles are on the whole smaller north than south of 

 Tallaton. 2 



Whatever may have been the exact physical conditions, all this 

 is quite consistent with a general south- to-north direction of the 

 current which brought the greater part of the materials. 



I have not attempted a discussion of all the problems connected 

 with the Lower Trias. My object has been rather to present certain 

 facts which, if correctly interpreted, may possibly help us to under- 

 stand other facts. But there is much yet to learn, and my purpose 

 will be served if the present paper should lead to further investi- 

 gations on the subject. 



I must acknowledge my great indebtedness to Prof. Bonney 

 for examining so fully the rock-specimens submitted to him, and for 

 permitting me to make use of his observations thereon. I am all 

 the more grateful to him for his help, because I know that he 

 strongly dissents from some of my conclusions. 



Discussion. 



The Chaieman (Mr. Teall) drew attention to the similarity of 

 liver-coloured quartzites and to their occurrence in conglomerates 

 of many ages. They were found in the Torridonian Sandstone 

 of the Xorth-West of Scotland, which clearly could not have been 



1 G. H. Morton, ' Isotes on the Bunter & Keuper Formations in the 

 Country around Liverpool,' Geol. Mag. 1890, p. 500. 



2 W. A. E. Ussher, Quart. Journ. Geol. Soc. vol. xxxii (1876) p. 367. 



