The Rev. Prof. Blake — Base of the Sedimentary Series. 357 



fit to give a more or less schistose character to the most solid igneous 

 rock. Yet the "evidence" on which Dr. Hicks "feels justified in 

 placing the whole of the so-called altered Cambrian of Moel Tryfaen 

 and the neighbourhood and the whole of the rocks . . . coloured as 

 intrusive felstone and porphyry .... with the Precambrian rocks," 

 is the schistosity of certain portions of a mass for which he can still 

 find no other general name than " felstones and quartz felsites," 

 together with " ashy " i - ocks of the same type, one of which, accord- 

 ing to Prof. Bonney, is a Cambrian conglomerate. This evidence 

 is manifestly insufficient. More convincing is Dr. Hicks's explana- 

 tion of the difficulties which seem to have prevented Prof. Ramsay 

 and even Prof. Sedgwick from perceiving that the conglomerates of 

 Llyn Padarn and elsewhere are derived from the rocks beneath them. 

 That they are so will probably be always henceforth acknowledged 

 in any interpretation of the district. But as to the nature of the 

 porphyry itself, we are left in no doubt by the examination of Prof. 

 Bonney, whose conclusion is irresistible that " they are neither 

 intrusive nor metamorphic in the ordinary sense of the word, but 

 parts of ancient lava-flows which, were they of modern date, we 

 should probably not hesitate to call rhyolites." But when we have 

 learnt this, we have not learnt all. Even a stream of lava must flow 

 upon something. Can we discover what that was ? If it wei - e true, 

 according to Dr. Hicks, that the conglomerates flank it on both 

 sides, the discovery would probably be hopeless. But Dr. Hicks 

 should really have more consideration for the legs of his brother 

 geologists than to write down such a statement without indicating 

 where it may be verified. It has given me many a mile's weary 

 tramp up and down the hills along their western border to find 

 any such conglomerate, but none have I ever found. From the 

 general slope of the whole series we should on the contrary expect to 

 find the bed of the lava-stream on the western side; and there, as I 

 have shown at Bryn-efail, we do find it, and see the lava tearing up 

 and altering the underlying slate and grit now turned on end. 

 Until this section is otherwise explained, we must admit that there are 

 Cambrian beds below the felsite, and the conglomerate cannot, how- 

 ever attractive the hypothesis, be the base of the series. It is 

 nothing wonderful that there should be a contemporaneous felsite 

 in the Cambrian rocks ; indeed the felsite of Moel Gronw is another, 

 and I have even seen one lower in the series in the valley near 

 Glanrafon south of Carnarvon. 



The third locality includes the various exposures of igneous 

 rock and the schistose beds on the west of the Lleyn Peninsula. 

 With regard to the latter, there is at all events, and always has 

 been, this common opinion, that whatever the Anglesey rocks are, 

 these are the same. But with regard to the igneous masses, it is 

 Dr. Hicks alone who is responsible for their Precambrian age. I 

 have already given evidence which shows that they cannot possibly 

 be so; to rebut which Dr. Hicks falls back on imaginai'y "thrusts." 

 I say " imaginary," because no evidence has ever been given of 

 their existence, and in one case at least — that of the Hinvain syenite 



