[Footnote 97: _Ibid._ p. 173.] [Footnote 98: _Mem. Geol. Surv._ vol. iii. 2nd edit. p. 173.] [Footnote 99: _Ibid._ p. 174.] No one who has examined this Caernarvonshire ground can have failed to find the sections which doubtless led my predecessor to form the convictions to which he gave expression in the passages I have just quoted. It is easy to see how these sections, wherein it is certainly difficult to draw a sharp line between the igneous rock and the clastic materials derived from it, would be welcomed as appearing to offer confirmation of the ideas concerning metamorphism which were then in vogue. There cannot, however, be any doubt that my friend was mistaken in his interpretation of the structure of that part of the country. It is to me a subject of keen regret that in his later years, when the subject was revived, he was no longer able to re-examine this ground himself, for no one would have confessed more frankly his error, and done more ample justice to those who, coming after him, have been able in some parts to correct his work. The quartz-porphyry, felsite or rhyolite of Llyn Padarn, as well as that of Llandeiniolen, is not a metamorphic but an eruptive rock, as has been demonstrated by Professors Hughes and Bonney. There is no true passage of the sedimentary rocks into it; on the contrary, the conglomerates which abut against it are in great part made out of its fragments, so that it was already in existence before these Cambrian strata were deposited upon it. These conclusions must be regarded as wholly indisputable. But most of the critics of the work of the Geological Survey have proceeded to certain further deductions. They have maintained that the presence of fragments of the porphyry in the overlying conglomerate marks an unconformability between the two rocks, that the conglomerate shows the base of the Cambrian system, and that the porphyry is therefore pre-Cambrian. These assertions and inferences do not seem to me to be warranted. They have, in my judgment, been disproved by Mr. Blake,[100] who shows that there is no break in the Cambrian series, that the various porphyries and their accompaniments are parts of that series, and that there is no certain proof of the existence of any pre-Cambrian rocks in the whole district.[101] [Footnote 100: In an excellent memoir read before the Geological Society in 1888, with the main conclusions of which I agree.] [Footnote 101: _Quart. Journ. Geol. Soc._ vol. xliv. p. 271. For subsequent papers by Mr. Blake, see _op. cit._ vols. xlviii. (1892) p. 243, xlix. (1893) p. 441.]