668 Geological Society. 
amygdules. The andesites consist of oligoclase and malacolite, 
embedded in a hyalopilitic groundmass containing palagonite, in 
which ilmenite, leucoxene, and magnetite are embedded. A table 
of the silica-percentages and specific gravities of the bedded rocks 
shows that a gap occurs between the ‘ northern rhyolite’ and the 
more acid of the andesite-tuffs that immediately follow; this, 
together with a discordance in strike, may indicate a break in 
voleanic history, a disturbed junction, or that this rhyolite is 
intrusive. From this point onward, the tuffs and lavas form 
a continuous series, despite the difference in the average silica- 
percentage of the andesite-group and the rhyolite-breccias. The 
tuffs thin to the north-eastward, their lapilli diminish in size, and 
they become more gritty and washed in aspect in the same direction ; 
facts which all point to the inference that the volcanic vent may 
have been to the west of the hill. The intrusive rocks are basic, 
and often amygdaloidal; they are granular or ophitic, and compare 
in composition with such olivine-dolerites as those of Rowley, the 
Clee Hills, and Little Wenlock, while they differ considerably from 
the intrusive dolerites of North Wales. 
2, ‘The Tertiary Fossils of Somaliland, as represented in the 
British Museum (Natural History).’ By Richard Bullen Newton, 
Esq., F.G.S. 
3. ‘The Caernarvon Earthquake of June 19th, 1903, and its 
Accessory Shocks.’ By Charles Davison, Sc.D., EGS. 
The Caernarvon earthquake of June 19th, 1903, was the pre 
earthquake indigenous to the county for more than five centuries. 
Its disturbed area contained about 25,000 square miles, and 
included nearly the whole of Wales, the North-West of England, 
the Isle of Man, and several of the eastern counties of Ireland. The 
centre of the innermost isoseismal (intensity 7) was situated beneath 
the sea, about 4 miles west of Pen-y-groes, and the longer axis of 
the isoseismal ran from N. 40° E. to 8. 40° W. It is concluded, 
from the seismic evidence, that the earthquake was caused by a slip 
of about 16 miles in length along a fault running in the above direc- 
tion, hading north-westward, and passing either through Clynnog 
or a mile or two either to the north-west or south-east. In the 
former case the fault-line might be submarine ; and itis pointed out 
that, if the fault which runs in a south-westerly direction from Aber 
to Dinlle (on the coast of Caernarvon Bay) were continued under- 
neath the sea to the neighbourhood of Nevin, it would occupy the 
position assigned to the parent-fault by the discussion of the 
earthquake-phenomena. 
The principal shock was preceded by an earth-sound, and followed 
by at least five shocks, originating apparently at the north-western 
extremity of the principal focus. In addition, six slight shocks and 
two earth-sounds were recorded by single observers ; and, if these 
be included in the earthquake-series, it follows that seismic action. 
was gradually withdrawn from the extremities of the focus and 
ultimately confined to its central region. 
