326 A. GEIKIE ON THE SUPPOSED 



The older foliation is seen in the bands that run from the lower 

 to the upper margin of the drawing. These bands have been dis- 

 rupted, and a second feebler foliation has been developed along 

 the lines drawn across the section from side to side. (See p. 318.) 

 Fig. 9. Microscopic section of spherulitic quartz porplryry, from Board 

 Schools, St. David's, viewed under polarized light, with crossed 

 nicols, X 25 diam. (See p. 315.) One of the large quartz 

 crystals appears in the upper left-hand corner. The beautifully 

 perfect spherulites are surrounded by the microcrystalline base. 



10. Ditto of spherulitic quartz porphyry, from below Nun's Chapel, 



St. David's, polarized light, crossed nicols, X 100 diam. This 

 drawing (magnified four times as much as fig. 9) shows the struc- 

 ture of one of the more finely spherulitic porphyries, the very 

 variable size of the spherulites, their isolation in the finely cry- 

 stalline base, and the presence of rounded blebs of quartz, one of 

 which appears on the left-hand margin of the drawing. (See 

 p. 315.) 



11. Ditto of granite frornBryn-y-Garn, polarized light, crossed nicols, 



X 25 diam, showing the distinctly granitic structure of the rock. 

 (See p. 313.) 



12. Ditto of a diabase dyke, showing fluxion-structure, from cove east 



of Nun's Chapel, X 50 diam. The upper part of the drawing 

 marks the zone of contact between the diabase and the stratified 

 rock ; and immediately beyond it the numerous well-formed plagio- 

 clase crystals appear, first parallel to the wall and then streaming 

 . round what was originally a crystal, possibly of hornblende, but 

 is now a mass of chlorite and other decomposition-products. (See 

 p. 323.) 



Discussion 

 (On Part I., March 21, 1883). 



The Pkesident remarked upon the great importance and interest 

 of the subject discussed in the paper. 



Dr. Hicks said that he commenced the study of these rocks in 

 1863, and afterwards carried on his researches in connexion with 

 a former Member of the Geological Survey (Mr. Salter), and in 

 consequence he was led to the discovery of the Menevian, Lower 

 Cambrian, and other faunas. He disproved Sir R. Murchison's 

 views that these fossils did not occur in the red rocks, and traced 

 fossils down to the base of the Cambrian. He pointed out that the 

 rock called by the Survey syenite, at Clegyr Hill, Nun's Chapel, and 

 elsewhere, was a stratified rock, fragments of which occur as pebbles 

 in the overlying conglomerates. He showed somewhat later that 

 the ridge of crystalline or granitoid rocks, with its altered beds on 

 each side, was Pre-Cambrian. Subsequently, with the aid of the 

 late Prof. Harkness, Mr. Davies, and others, he was able to show 

 that the granitoid rock was not intrusive, but had more the character 

 of a metamorphic rock. The author of the present paper had mis- 

 taken some of his statements, which referred to N. Wales and 

 Anglesey, as applying to St. David's. He thought that these so- 

 called syenites had more of the peculiar characters of true granitoid 

 rocks ; and this was esp ecially shown by their peculiar fracture. 



