PRE-CAMBRIAN ROCKS OF ST. DAVID'S. 327 



He remarked on the general parallelism of the igneous intrusions 

 along beddirig-planes' in great formations, and on their presence 

 in the Dimetian as having a bearing on the probable strike in that 

 formation. He proceeded to criticise the sections as given, which, he 

 said, were not borne out by the actual facts, as he could vouch for 

 from a thorough knowledge of the district. Professor Bamsay had 

 agreed with him as to the great amount of faulting near Porth-clais; 

 but Prof. Geikie admitted no faults. He instanced the special section 

 cited at the Allan valley as illustrating the ignoring of faults by 

 the author; and he produced specimens from the point to show there 

 had been no alteration from the supposed intrusion. On the theory 

 of intrusion, how could the presence of the conglomerates at Ogof- 

 Llesugn be accounted for ? These conglomerates are not more altered 

 than those frequently found at a distance from the Dimetian ; but 

 the author had been deceived by the effect of crushing, and by an 

 appearance due to the fact that the matrix was the recemented 

 arkose-like material derived from the denudation of the Dimetian. 

 With respect to the porphyry of Nun's Well, he had himself figured 

 it as an intrusive rock, but had shown that it does not penetrate the 

 Cambrian conglomerates. He pointed out that a large area of 

 quartz porphyries near St. David's had been quite overlooked by the 

 author; and that the great so-called intrusive band in the Survey 

 Map of 1857 is made up of quartz felsites, breccias, and sedimentary 

 beds, that its boundaries are incorrect, and, he was now compelled to 

 say, that many other masses in the district are equally wrongly 

 coloured and defined in that Map. The junction at Ogof-Llesugn 

 and at Porth-lisky was clearly not an intrusive, but a faulted junction. 

 At Porth-lisky the unconformity between Pebidian and Dimetian 

 was manifest. On the western side of the district the unconformity 

 of the Cambrian is proved by an overlap of the series below. 

 The so-called tuff in the Cambrian he had examined, and found 

 to be merely derivative from the underlying Pebidian rocks. Other 

 bands he had shown to be intrusions along bedding-planes. 



Mr. Toplet said that he had had the advantage of visiting the 

 district with both Dr. Hicks and Mr. Geikie. He had great difficulty 

 in discriminating between joints and so-called bedding-planes in the 

 Dimetian and Arvonian when he visited the district with Dr. Hicks. 

 He admitted many errors in the old Geological Survey Map, which are 

 due to the hasty way in which it must have been constructed. He 

 confirmed Mr. Geikie's views as to the section at Porth-clais. With 

 regard to the Pebidian, Dr. Hicks admitted a general conformity 

 of strike ; and he (Mr. Topley) could not admit that the presence of 

 a few fragments of the underlying volcanic rocks in the Cambrian 

 quartzite conglomerate had the significance insisted upon by the 

 advocates of the Pre-Cambrian. The author of the paper had 

 shown the presence of contemporaneous volcanic tuff in the un- 

 doubted Cambrians. The same metamorphism has affected both the 

 Cambrian and the underlying beds. He believed that Prof. Ramsay's 

 old views would in the end prevail. 



Mr. T. Davies found, on reexamining his sections of Dr. Hicks's 



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