I02 PROCEEDINGS OF THE GEOLOGICAL SOCIETT. 



the quartzite contains fragments of the volcanic rocks, but, as I have 

 already pointed out, such a fact is of little value in establishing 

 an important break between a group of volcanic and one of ordi- 

 nary sedimentary rocks*. According to present evidence, the 

 volcanic group may most naturally be regarded as a part of the 

 Cambrian series. 



N'ot many miles to the north-east, in the Charnwood-Forest dis- 

 trict, numerous isolated protrusions of ancient rocks rising from 

 among the red sandstones and marls of the great Midland Plain 

 have long given rise to speculation among geologists. They were 

 regarded as of Cambrian age by the Geological Survey, and they 

 have since been carefully studied by Professor Bonney and the Rev. 

 Edwin Hill t- I allude to them here because they include a group 

 of undoubtedly volcanic materials such as ashes and agglomerates. 

 Their true geological relations can hardly be demonstrated, for they 

 are surrounded by much younger rocks, but there seems some pro- 

 bability that they belong to the same series as that of Nuneaton, 

 and that they may thus bear additional testimony to the volcanic 

 activity which marked the Cambrian period in this country. 



One other volcanic area requires notice here — that of St, David's, 

 in South Wales. Though, for the sake of geographical continuity, 

 I have deferred its consideration until after the description of the 

 corresponding tracts in North Wales and the west and centre of 

 England, it was the first district where volcanic rocks of contem- 

 poraneous origin were shown to underlie strata of Cambrian date. 

 It has received a large amount of attention from geologists, mainly 

 owing to the labours of Dr. Hicks, who was led to recognize the true 

 volcanic character of the deposits below the fossiliferous Cambrian 

 rocks. He named them Pebidian, regarding them as pre-Cambrian 

 and as separated by an unconform ability from the base of the 

 Cambrian system. Much discussion has arisen over his interpre- 

 tation of the structure of the district J. Having already entered 

 the lists with him, I shall avoid here any renewal of the contro- 

 versy, confining myself to mere reiteration of views which I have 



* Lapworth, Geol. Mag. (1886) p. 319 ; T. H. Waller, loc. cit ; A. Strahan, 

 op. cit. p. 540. X 



t Quart. Journ. Geol. Soc. vols, xxxiii. (1877) p. 754, xxxiv. (1878) p. 199, 

 xxxvi. (1880) p. 337. 



+ See especially Hicks, Quart. Journ. Geol, Soc. vols, xxxi., xxxiii., xxxiv., 

 xl. ; Geikie, op. cit. vol, xxxix, (1883) ; Blake, op. cit. vol. xl. (1884) ; Lloyd 

 Morgan, op. cit. vol, xlvi. (1890), 



