330 A. GEIKIE ON THE SUPPOSED 



to many of the objections. He disclaimed any idea of charging 

 Dr. Hicks with acting unfairly ; he thought he had made a mistake. 

 M. Eenard agreed with himself as to the non-gneissic character of 

 the so-called Diinetian. He thought Dr. Hicks would himself be 

 prepared to give up the Arvonian. He saw no reason why fossils 

 should not be found in stratified volcanic tuffs of the so-called 

 Pebidian. The conglomerates do not contain the characteristic rocks 

 of the St. David's district. He deferred further reply till his 

 second part was read. 



Discussion 

 (On Part II., April 11, 1883). 



The President asked for a calm and judicial discussion of the 

 weighty problems treated of in the paper. 



Dr. Hicks stated that since the last meeting he had revisited the 

 district with Prof. Hughes and ten excellent trained observers from 

 Cambridge. This examination confirmed to the fullest extent the 

 views expressed by Prof. Hughes and himself at the last meeting, 

 and it proved also that the supposed facts relied upon by the author 

 to support his views were clearly mistakes made by the author from an 

 imperfect acquaintance with the district and the rocks. By the admis- 

 sion of the author the appearances are abnormal in the St. David's area. 

 With respect to the intrusive character of the so-called granite, he 

 asked what had become of the materials displaced by the intrusion. 

 He regarded the so-called tuffs alternating with the Cambrian con- 

 glomerates as derivative rocks, full of quartz-grains &c. The junc- 

 tion of the sedimentary rocks with the granitoid rock was a faulted 

 and not an intrusive junction. The fault was marked by slicken- 

 sides, but not by any contact metamorphism. He demurred to the 

 author's views as to the double series of foliations. He showed 

 that while a dyke of greenstone 50 yards wide had produced 

 enormous alteration in the surrounding rocks, the great granitoid 

 mass had produced no alteration. At Ogof-llesugn, a place speci- 

 ally referred to by the author, it was possible to get between the 

 Dimetian and the quite unaltered Cambrian conglomerate. Another 

 mass of conglomerate was jammed in through the action of a fault. 

 The amount of faulting and crushing in this area was enormous — a 

 fact which did not seem to have been recognized at all by the 

 author of the paper. The supposed porphyries in the Pebidian were 

 really for the most part indurated ash. The author now admitted 

 that unconformity existed between the Pebidian and the Cam- 

 brians. Examined with more care than appeared to have been 

 given to it by the author, the conglomerate was found to consist in 

 very large part of the Pebidian rocks, and of derivative materials 

 from the still older Arvonian and Dimetian series. This fact was 

 remarkably confirmed in Eamsey Island. He maintained the ex- 

 istence of a great unconformity between the Pebidian and the Cam- 

 brian conglomerates, the materials of the former having been meta- 



