244 



PEOF.C. LLOTD MORGAN ON THE PEBIDIAN 



of these localities severally and then the evidence afforded by the 

 materials of vs^hich the Cambrian conglomerate is composed. 



b. In Caerhivcly Valley. — This locality is situate about a mile to the 

 south-east of 8t. David's city. The conglomerate is here seen crossing 

 the valley, striking N. 65° E., and dipping seawards somewhat 

 steeply. It is underlain by a close-grained red felspathic tuff. 

 There is no sharp line of demarcation between the two, and a good 

 deal of evidence that the felspathic tuff is inwashed into the con- 

 glomerate. Some three or four feet above the base of the conglo- 

 merate, for example, a very similar material occurs *. On the east 

 side of the valley this tuff crosses the road, and associated with it 

 there seems to be a more argillaceous line-grained tuff of a pink 

 colour. The strike here appears to be the same. Higher up the 

 valley bedded porcellanites are well exposed in a quarry. Their 

 strike can be accurately read ; it is the same as that of the con- 

 glomerate, iS^. 65° E. 



Erom Caerbwdy Valley westwards the conglomerate does not 

 afford facilities for observation until we reach St. Non's Bay. 



Eig. 1. — Sketch-map of St. lion's Bay. (Scale 1 foot to 1 mile.) 



1 1 Diabase dykes. 



Conglomerate. 



•-I--I--I-+ Quartz-porphyry dykes. 



Cambrian (Caerfai beds). 





■jtj: Pebidian. 



a-e. Faults. 



c. In St. Nan's Bay. — This locality is situate south of St. David's 

 city, about a mile west of Caerbwdy Valley. If we approach the 

 bay from Brjoi-y-garn, skirting the field in which St. Non's Chapel 

 stands in ruins, we find ourselves at the head of the most westerl}' 

 of the series of little creeks shown in the sketch-map, fig. 1. Skirting 

 this and standing at the point marked oj we obtain the view shown 

 in fig. 2. Along the central line of vision runs the conglomerate, 

 striking N. 75° E., and forming the northern side of an arch (St. 



■^ Although the microscopic character of the rock is obscure, still the micro- 

 scope only reinforces the macroscopic similarity. 



