ANGLESEY AND CAERNARVONSHIRE. 191 
by his own statements, will be compelled to grant that our views are 
correct, and that he and his predecessor have been completely in the 
wrong in their interpretation of the geology of those areas, so far at 
least as the oldest rocks are concerned. The following statement occurs 
at p. 305 of the paper already referred to :—‘ There can be no doubt 
that conglomerates frequently mark the natural base of a series of 
sedimentary deposits. ‘They do so more especially where they are 
formed of materials that have had an obviously local origin, and 
where they rest unconformably on the rocks below, from the waste 
of which they may have been mainly derived. In such cases they must 
be regarded as littoral deposits ; and in this respect they possess im- 
portance from the light they throw on former geographical con- 
ditions. Of other conglomerates which possess local value as strati- 
graphical horizons only, he says—‘‘ Unlike the basal conglomerates 
just referred to, they are composed of well waterworn pebbles, for 
the most part comparatively small in size, derived from some distant, 
and in many cases, unknown source, and consisting usually of quartz, 
quartzite, or other exceptionally durable rocks.’ TI accept to the 
fullest extent the tests suggested by the Director General in the above 
quotations, and I now submit the facts to the Society, feeling confident 
that the verdict must be in our favour. As the Director General 
has acknowledged that we are correct in placing the Pebidian rocks 
below the basal conglomerates, as a great volcanic series, though Sir 
A. Ramsay maintains that the oldest volcanic rocks known in 
Britain (as may be seen by referring to his Address as President of 
the British Association in 1880), of which he had any personal 
knowledge, are of Lower Silurian age, I will only refer to those 
rocks so far as it may be necessary to point out evidence of their 
Pre-Cambrian age, by showing the Cambrian Conglomerates resting 
unconformably upon them, and being here and there made up 
very largely from their denudation. It is more important that in 
this paper I should confine myself to the above-mentioned rocks, 
which are claimed by the Surveyors as irruptive masses of a date 
long posterior to the deposition of the Cambrian Conglomerates, 
which now surround them. 
Llanfaelog, Anglesey. 
In my paper of 1879 I pointed out that the so-called intrusive gra- 
nite as exhibited near Llanfaelog, in Anglesey, was almost identical in 
character with the Dimetian granitoid rocks at wt Hill, Caernarvon, 
the so-called Rhos Hirwain syenite, and the Dimetian at St. Davids ; 
and my views were fully confirmed by Professor Bonney’s examina- 
tion of the rocks in the field and under the microscope. Imaintained 
that this so-called granite patch, instead of being, as stated by the 
Surveyors, composed of granite intruded into the Cambrian and 
Silurian rocks in Lower-Silurian time, and of metamorphosed and 
entangled portions of those rocks, actually consisted of the 
oldest rocks in Anglesey, and formed an old axis not only to the 
Cambrian and Silurian rocks, but even to the newer of the Pre- 
