﻿296 THE ST. DAVID's-HEAD ' EOCK-SEEIES/ pJ^^Y I908, 



it seemed improbable that that of the St. David's-Head rocks 

 corresponded ^ith any of thera. The Author had observed that the 

 complex had suffered no morement since its consolidation, and in 

 view of the extensive post- Carboniferous disturbances which had 

 affected the district to the south-east the speaker considered that 

 the intrusion most likely took place in post-Carboniferous time. 



The Author, in reply, thanked Dr. Flett for his interesting 

 remarks on the recurrence of eruptions of similar types of rock in 

 different geological periods, and he was glad to have his support 

 with regard to the nomenclature of the rocks, and other points 

 mentioned in the paper. As to the relative order of crystallization 

 of enstatite and augite, alluded to by ^Lr. Allan Thomson, the 

 view of Prof. Togt, that the separation of augite before enstatite was 

 impossible on theoretical grounds, referred particularly to iron- 

 free enstatite, and not to the ferriferous varieties described in the 

 paper. In reply to Dr. Hatch, he said that the felspars in the aplite- 

 veins appeared to be solely albite. "With respect to Mr. Eailey's 

 reference to non-consolute magmas, this theory certainly had support 

 from recent discoveries in physical chemistry, but the evidence in the 

 St. David's-Head intrusions scarcely warranted the assumption of a 

 separation of the magma into two or more non-consolute magmas 

 in sifu. Mr. Thomas referred to the possible age of the intrusions, 

 upon which the Author's evidence was admittedly obscure, the 

 only clear point being the complete absence of any sign of earth- 

 movements since the conso]idation of the rocks in question. In 

 conclusion, the Author thanked the Pellows for their kind reception 

 of his paper. 



