290 Reports and Proceedings : 
are traceable along the south and north sides of the trap-region, and 
are followed by sandstones of various degrees of coarseness, but 
indicating by the ripple-mark, as well as the coarse material, that 
they were accumulated in shallow water; and, as we know that 
pebbles, often as large as swan’s eggs, are not carried far out to sea, 
but mark either a submarine shoal or a coast-line, we are compelled 
to assign them to a source near at hand. ‘The upper beds of the 
Lower Cambrian formation are finer-grained and lighter-coloured, 
and pass insensibly into grey and then into thin black beds of the 
Lingula-flags, with trappean ashes and lava-flows,—the great Upper 
Cambrian formation. 
Comparing this order of things with what occurs in North Wales, 
one is struck with the wonderful similarity in the two regions; 
coarse conglomerate and purple shale, red sandstones, and then grey 
rocks, passing into black, deep-water shales. Crossing the channel, 
it is the same; the Lower Cambrian rocks of Wicklow give evidence 
of accumulation in shallow water; and Sir R. I. Murchison has 
shown us exactly the same thing, even exaggerated, in the con- 
glomerates of north-western Scotland ; but these rest directly on the 
old Laurentian rocks, from which they seem to have been derived. 
The Hebrides and the west coast of Sutherland were land or shallow 
water when the Cambrian pebble-beds were formed around them. 
We do not know the land which supplied the pebble-bands and sand- 
stones of North Wales and Shropshire; but the researches of Dr. 
H. B. Holl have shown us that the Malvern Hills were a low reef of 
rocks at this time; and everything points to a shallow sea, studded 
with islets and reefs, as the condition of things which existed in our 
area, probably also in Normandy and the Channel Islands, at this 
time. Again, the old Laurentian gneiss is remarkable for its syenitie 
character. Syenite is common; true granite is comparatively rare 
in these old rocks. This is the case in Canada, where they are best 
seen. Dr. Holl has shown it to be the case at Malvern, and hence 
we should look for it in Wales. The mass of igneous rock, which 
forms the back bone of the St. David’s peninsula, and which sup- 
ports, without penetrating them, the shallow-water accumulations of 
the older Cambrian around it, is syenitic in character. The quartz- 
veins penetrating it may well have supplied the pebbles; and the 
felspathic matter was the origin of the softer schists of the rocks 
which le around it. That there was shallow water, with rocky 
ground close by, is evident; and in the absence of any evidence to 
the contrary, the author suggests that the syenitic trap of St. David’s 
is a part of the old pre-Cambrian land. As he did not visit Ramsey 
Island the evidence is incomplete. It will be necessary to see 
whether the Cambrians there are affected by the trap, or lie upon it 
unaltered, as he believes is the case with those of St. David’s. 
On tHE Wuirr Lias or Dorsetsutre. By Dr. Wricut, F.R.S.E., F.G.S. 
rFVHE author first gave a sketch of the Lias formation as displayed 
in the grand coast-section between Down Cliffs and Pinney 
Bay, on the coast of Dorset, in which all the different beds of the 
