[Illustration: Fig. 44.--Section of Clegyr on the north-east side of Llyn Padarn, near the lower end.] But we have evidence that, during the period when these showers of volcanic detritus were thrown out, streams of lava, though on a greatly diminished scale, continued to be poured forth. The hill of Clegyr (Fig. 44), near the lower end of Llyn Padarn, on the north-east side, consists mainly of cleaved tuffs (_t_) and slates with conglomerates (_c_), overlying the quartz-porphyry (_p_). Near the summit a band of felsite is intercalated in these rocks. Still more striking are the sections on the south-west side of the lake.[112] Starting from the porphyry of the ridge, we cross a zone of conglomerate and grit largely composed of the debris of the porphyry, until we reach a band of felsite or quartz-porphyry, which at its eastern end is about ten feet thick, while it seems to increase in dimensions westwards.[113] In the centre the rock is dark purplish-red, exceedingly compact or flinty, sprinkled with a variable proportion of quartz-blebs and felspar crystals. Towards its southern or upper edge (for the rocks, though nearly vertical, dip southwards) it has been cleaved into a variety of purple slate, and would there at once be classed among the ordinary slates of the neighbourhood. But the fissile character is merely a marginal structure which the rock shares with the highly-cleaved tuffs that follow it. Traced westwards, this bed is found to enclose a core of quartziferous porphyry, which, though it has escaped from the most complete results of crushing, is nevertheless cleaved along its margin as well as partially in its interior. It would not be possible to distinguish parts of this intercalated less crushed core from portions of the porphyry of the main ridge. The difference of colour does not count for much, for even in this core the purple tint gives place to greenish grey, and what in the centre at the east end is a solid dark purplish-red felsite passes westward into a greenish slate, like that already noticed on Mynydd y Cilgwyn. [Footnote 112: For various readings of these sections, compare Mr. Blake (_Quart. Jour. Geol. Soc._ vol. xlix. (1893), p. 450) with Professor Bonney and Miss Raisin (_op. cit._ vol. l. (1894), p. 581).] [Footnote 113: See Professor Bonney and Miss Raisin, _op. cit._ p. 593 _et seq._]