H. HICKS ON THE rRE-CAMBRIAN ROCKS OF ST. DATId's. 241 



like organisms in the specimens referred to by Mr. Hicks, but 

 thought that fossils would probably be found in the series by and 

 by. He described the beds passed through in the adit to the slate- 

 quarry on Moel Trj-faen, south of Caernarvon, and thought there 

 was much reason for considering them Pre-Cambrian ; but they 

 appeared to him to resemble more the Dimetian of Mr. Hicks than 

 the Pebidiauc beds. 



Mr. Ethekidge said that these rocks of St. David's are so special 

 that the author was justified in proposing new names for them. 

 He confirmed the author's statement as to the extent of the faults 

 in Ramsey Island. 



Mr. Hudleston wished to call attention to the character of some 

 of the rocks to which Mr. Hicks had alluded, and more especially to 

 a class of rocks called "dolomites," which occurred in beds of mode- 

 rate thickness. The specimen examined was not a true dolomite, 

 but rather a calci-dolomite, the proportion of lime being too great. 

 Moreover, with the carbonates were mixed silicates of probably no 

 very definite constitution. With these was associated a moderate 

 amount of a serpentinous or chloritic substance which pervaded the 

 rock, and was more plentiful and better defined in some other spe- 

 cimens. Such a rock was evidently now much altered from its 

 original state ; and there were two alternatives which seemed to 

 present themselves ;. either we had here a rock which had, perhaps, 

 been broken down from a highly crystalline state ; 01% what was far 

 more likely, its present condition was the result of alteration from a 

 marly and gritty mud, whose original constituents had arranged 

 themselves into crystalline forms more or less complete according to 

 their several affinities. 



Rev. H. H. \Vixwood objected to the term Pebidian as being 

 merely derived from the name of a Hundred, and not possessing any 

 generally intelligible connexion with the locality in which the rocks 

 in questftm occur. 



The Author, in reply, stated that the names used by him were 

 local and applied to the district. He considered that the succession 

 of the Scotch rocks was not well determined, and that therefore 

 they could not yet be correlated with the Welsh deposits. 



Q. J. G. S. No. 130. r 



