﻿382 ilE. J. F. Jf. GREEN ON THE GEOLOGICAL [Aug. I908, 



(3) The process of mapping has shown clearly that there is a 

 strongly marked unconformity between the Pebidian and 

 the overlying Cambrian. 



(4) The St. David's granophyre (Dimetian) is probably a laccolite, 

 terminating along one edge at least in a sill-like prolongation 

 clearly intrusive in the Pebidian. The post-Pebidian age of 

 the whole is thus established. 



(o) The actually observed junctions of the granophyre and the 

 Cambrian are all faults — except in one case, where, on being 

 cut open, the conglomerate is seen resting upon the eroded 

 surface of the Dimetian, Ko trace of contact-action has been 

 seen anywhere at the junction of these two rocks. The pre- 

 Cambrian age of the granophyre is thus clear. 



(6) Xo basic lavas have been met with in this area, those 

 forming the • stacks ' being clearly of an intrusive nature and 

 of post-Cambrian, if not of post-faulting, age. 



The pre-Cambrian age of Dr. Hicks's Pebidian being so clearly 

 proved, it seems only just that the name should be revived, if not 

 indeed extended to other areas, as he suggested. The contem- 

 poraneity of the series with similar rocks of pre-Cambrian age in 

 other areas cannot be claimed as definitely established; but, if any 

 general name is applied to these rocks, such as those of Charnwood 

 and the TJriconian, Dr. Hicks's term should have priority. 



The friends at St. David's who have shown me kindness are too 

 numerous to mention; but I must name Mr. H. P. Jackson, Master 

 of the Secondary School, and Mr. William Davies, of Ehoscribed 

 Farm, who kindly granted permission to dig a trench on his land 

 and afforded us much useful information. Above all, I owe to 

 Mr. George Barrow, not only the original suggestion that I should 

 attack this complex area, but constant assistance and advice which 

 alone made the production of this paper possible. 



EXPLANATION OF PLATE XLIV. 

 Geological map of the St. David's area, on the scale of 3 inches to the mile. 



Discussion. 



The CHAiEiiAN (Dr. Teall) referred to the keen controversy that 

 had taken place in that room about a quarter of a century ago on 

 the subject of the St. David's rocks, and remarked that the Author's 

 very careful work tended to show that both the combatants were 

 right and both were wrong. 



Mr. Baeeow drew attention to the gradual advances in our 

 knowledge marked by the present paper. When Hicks began work 

 at St. David's, the geologists of his day often took the faint 

 foliation of such rocks as the Dimetian for the last trace of bedding 

 in an intensely-altered sediment ; and, holding this view, they 



