VOLCANIC SEKIES OF ST. DAVIDS. 267 



but in any case to be included under the Palaeozoic and not under 

 the Archaean category. 



These beds, in the western part of the district, where they can be 

 best studied, are thrown into a series of three folds — a northern 

 anticline, a central syncline, and a southern anticline folded over to 

 form an isocline with reversed dips to the south-east. The axis of 

 folding is roughly parallel with the axis of St. David's promontory. 



There is no evidence in the district of an Arvonian system. 



The Dimetian is intrusive in the southern limb of the isocline. 



There are no Archaean rocks at St. Davids, unless some of the 

 included fragments in the Pebidian tuffs arc to be so regarded — in 

 any case no Archaean rocks in situ. 



EXPLANATION OF PLATE X. 



Sketch Maps of the North- western and South-western portions of the 

 District of St. Davids, on a scale of six inches to the mile. 



The brokoi lines between the two Maps unite the points at which they 

 fit together. 



Discussion. 



The President commented upon the differences of opinion among 

 those who had studied the geology of St. Davids, and pointed out 

 that there were two points of primary importance — the relations of 

 the Pebidian to the Cambrian, and those of the Dimetian to all the 

 other rocks. The Arvonian question was of less consequence. 



Dr. Hicks said that the Author had commenced his paper with a 

 reference to the Caerbwdy valley, but had not referred to the great 

 agglomerates at Clegyr, nor to the clearly bedded porcellanites. 

 ]N'ow, there was nothing porcellanized in the Cambrian, and yet 

 fragments of the Pebidian porcellanite abound in the Cambrian 

 conglomerate. He proceeded to describe the different beds ou which 

 the conglomerate rests transgressively, showing how the Pebidians 

 vary in character at different points ; he also commented on the 

 absence of a map, and the paucity of sections. As to that at 

 St. Non's Arch, the unconformity on the porcellanites was clearly 

 shoAvn in both interpretations, and he exhibited photographs in 

 proof of the correctness of his own reading of this section. At Ogof 

 Golchfa the Author had sliown the beds as almosit conformable, but 

 photographs were entirely against this interpretation. There might 

 be a kind of crush here between the Cambrian and Pebidian, as 

 would happen at the junction of such dissimilar beds ; but there 

 was no fault, only a shearing. At Khoson and other places large 

 fragments of Pebidian had been found, which showed that they had 

 been cleaved before being enclosed in tho conglomerate. 



Criticizing the diagrammatic section exhibited. Dr. Hicks remarked 

 that he himself had once given a similar section, but had found that 

 such a simple interpretation was impossible, and that the beds of 

 the Pebidian had been greatly broken and, in places, inverted, as the 



