£94 REV. J. F. BLAKE ON THE 
21. On the Voucanic Grove of St. Davin’s. 
By Rey. J. F. Buaxs, M.A., F.G.8. (Read January 9, 1884.) 
Tue discordant views which at the present moment prevail on the 
subject of the oldest rocks in the St. David's district, and the interest 
which attaches to these rocks according to one at least of the inter- 
pretations, induced me, after a visit to the Highland regions on which 
the same discordance is shown (but where nature seemed to differ 
widely from her earlier and disputant interpreters), to attack the 
St. Dayvid’s problem independently, and to stay in the district long 
enough to come to a conclusion as to the true nature and age of the 
rocks. 
Finding myself in accord neither with Dr. Hicks on the one hand, 
nor with Dr. Geikie on the other, but led irresistibly to the more 
simple results so ably shadowed forth by Mr. Hudleston*, I cannot 
retrain from offering to the Society the evidences on which my 
conclusions are based; as I cannot suppose that the reply which Dr. 
Hicks will doubtless produce, will represent the same and, as I 
believe, the true view of the question. 
The result of my observations may be thus briefly stated :—-all 
the rocks which have been designated Dimetian, Arvonian, and Pebi- 
dian, round and near the city of St. David’s, belong to one volcanic 
series, Whose members are those usually recognized in eruptive 
areas, and whose age is anterior to and independent of the true 
Cambrian epoch. 
An a priori argument in favour of this view is, that it unites the 
essential features of both the other interpretations; it has the 
advantage of simplicity, and renders a reason for the constant 
association in the other Pre-Cambrian areas of three types of rock 
which may be interpreted in the same manner. Nevertheless, were 
the foeman deemed worthy of the steel, it would doubtless meet with 
strong resistance from the holders of either of the previous views, as 
it coincides with neither. 
The first point that stands in need of proof is the entire indepen- 
dence of every member of the volcanic series and the Cambrian rocks 
from the conglomerate upwards. ‘Their junction can be studied in 
one way or another round most of the circuit, as seen in the map 
(fig. 1), and can only be satisfactorily explained by the occurrence of a 
series of bounding faults, such as would be produced when the under- 
lying mass was forced up amongst the newer rocks at the time when 
their nearly vertical position was assumed. 
On some parts of this circuit I need but briefly touch, merely 
corroborating what has been said by Dr. Hicks and others. Starting 
at the south of St. David’s, the line of junction first comes to day 
in a little bay to the west of the ruins of Nun’s Chapel, where 
* Quart. Journ. Geol. Soc. vol. xxxiy. p. 167. 
