VOLCANIC GROUP OF ST. DAVID’S. oh 
Mr. Topley had called attention. He asked Prof. Blake to explain 
how the ashy beds could form one series with the granites. 
Mr. Huvzxstron said that the difference of the Dimetian from 
granite might be from subsequent alteration, as the Roche-Castle 
rock had been altered. What was wanted was proof of a passage 
from the Dimetian to the quartz-felsites. 
Prof. Bonnry said that he should confine his remarks mainly to 
the petrology, for as regards the stratigraphy it did not appear 
to him that Mr. Topley’s criticisms were serious. It appeared to 
him not to be so simple a matter as Prof. Blake supposed, to say 
whether the Dimetian was granite or not; certainly it differed 
from all typical granites, and the difference could not be explained 
as Mr. Hudleston suggested. We could not, in questions of this 
kind, where felsites distinctly broke through granitoid rocks which 
were In some cases certainly of metamorphic origin, leave other 
Archzan areas out of consideration, and he certainly thought that, 
whether granite or not, the Dimetian was much older than the 
felsites and ashes. 
Prof. Braxer said that the Dimetian differed much from Hebridean 
eneiss. He replied to Dr. Hicks’s criticisms of his map that they 
would not affect his views. There might have been intervals be- 
_ tween the members of this Pre-Cambrian group, as he could not 
absolutely prove the passage of one into the other, but still he 
thought it simpler to regard them as one group. He thought 
that the unconformity, whether it were above volcanic rocks or not, 
was important. 
