[Footnote 109: The sections in the Vale of Llanberis on either side of Llyn Padarn have been again and again described and fought over. Some of the papers are cited in the following pages, but it would be impossible in this volume to find room for a full discussion of the differences of opinion. What is stated in the text is the result of my own study of the rocks on the ground, coupled with a careful consideration of the work of other observers.] [Footnote 110: I can find no evidence of unconformability beneath any of the conglomerates. The section described by Professor Green, _Quart. Journ. Geol. Soc._ vol. xli. (1885), p. 74, merely shows the difference between the effects of cleavage on the fine tuffs and the more massive resisting conglomerate which overlies them. This section is represented in Fig. 43. At first sight the conglomerate appears to be lying on the vertical edges of an older group of slates, but any one acquainted with cleavage can trace this structure from the tuffs into the conglomerate and resuming its course again in the finer sediments above. The whole series of deposits in the section is continuous and conformable. The section on the slate railway has deceived Mr. Blake as well as Professor Green (_Quart. Journ. Geol. Soc._ vol. xlix. (1893), p. 445). The correct interpretation is given by Professor Bonney and Miss Raisin (_op. cit._ vol. l. p. 592).] One of the first features of these detrital deposits to arrest attention is the amount and variety of the fragments of igneous rocks in them. Some of the conglomerates, though enclosing pebbles of quartz, quartzite, granite and other rocks not found _in situ_ in the immediate district, are mainly composed of the debris of the quartz-porphyry of the ridge. Indeed, this latter material appears to have contributed a large proportion of the detritus of which the general body of strata here is made up. But there are to be noticed among the contents of the conglomerates and breccias pieces of many volcanic rocks not to be found on the porphyry ridge. Among these, besides felsites showing sometimes beautiful flow-structure (rhyolites) and various quartz-porphyries, there occur abundant fragments of less acid lavas (andesites) and pieces of older tuffs. Some of the fragmental rocks are green in colour, probably from the abundance of fine basic volcanic dust in them. Certain bands are full of large angular pieces of shale, similar in character to the Cambrian slates, and doubtless due to the disruption of pre-existing Cambrian strata by volcanic explosions. It is clear that from vents in this neighbourhood there continued to be an abundant discharge of dust and various andesitic and other lapilli, which, falling on the sea-floor, mingled there with the ordinary mechanical sediment that was being deposited at the time.[111] [Footnote 111: On the composition of the conglomerates or breccias, see Professor Bonney and Miss Raisin, _Quart. Jour. Geol. Soc._ vol. l. (1894), p. 598.]