518 H. HICKS ON THE PRE-CAMBRIAN 
exhibited by the rocks of this group remain sufficiently accurate ; 
but in addition to the quartz-felsites (old rhyolites), breccias, and 
hiilleflintas mentioned, I have noticed also in some of the areas, as 
in South Pembrokeshire and in the area to the N.E. of St. David’s, 
rocks which appear to be indurated argillites. 
The latter show clear evidences of aqueous deposition during the 
period ; and the fragments which occur in the basal Pebidian agglo- 
merates point out that induration had taken place, to some extent 
at least, in these argillites before the agglomerates of the Pebidian 
were accumulated. It is highly important that the peculiar characters 
exhibited by the Arvonian rocks should be clearly understood, and 
that the fragments in the lower Pebidian breccias should be iden- 
tified with rocks now exposed in the area. ‘The evidence obtained 
in this way is perfectly conclusive in showing that there are acid 
lava-flows in the area which must be of older date than the 
Pebidian rocks. And yet the Director-General says at p. 300:— 
‘‘ All the siliceous eruptive rocks, so far as I have been able to dis- 
cover, are intrusive, and belong, I believe, to a much later period 
than that of the volcanic group; in no single instance did they 
appear to me to be true superficial lava-flows.” Dr. Persifor 
Frazer, of Philadelphia, who visited the St. David’s sections under 
Dr. Geikie’s guidance, says, however, on the other hand, in a paper 
published by him last year *, that the Pebidian breccia immediately 
to the west of Clegyr Foig rock ‘‘seems to be a remade rock, in- 
cluding within itself fragments of ortho-felsite, which would fix its 
origin as later than the latter.” 
Though this group consists so largely of volcanic materials, it 
seems to me, from all the evidence I have been able to collect, to 
belong to a period anterior to that during which the Pebidian 
rocks were accumulated or deposited; hence some such a name as 
Arvonian is necessary to indicate the geological position of the group. 
VII. Tur Pesiptan Rocks. 
a. Hvidence as to Age-—In my previous papers much evidence 
was given to show that the Pebidian rocks were older than the 
Cambrian rocks; also that the latter were very largely indeed built 
up of materials derived from the former, and that the basal Cam- 
brian conglomerates not only overlapped the Pebidian rocks uncon- 
formably, but were found to be almost at every point in contact with 
different members of the Pebidian series. I was therefore much 
surprised to read the statements made over and over again by the 
Director-General in his paper, that the Pebidian is only a part 
of the Cambrian, and, as at p. 291, that it “passes regularly 
upwards into the fossiliferous Cambrian formations, from which it 
cannot be dissevered, and with which it must be classed.” 
Ample evidence will be given, in speaking of special areas, to 
prove that the Pebidian rocks must undoubtedly be of much older 
“ A Comparison of the Eozoic and Lower Paleozoic in South Wales with 
their Appalachian Analogues in the United States,” 1883, p. 10 (Trans. American 
Inst. Mining Engineers). 
