536 H. HICKS ON THE PRE-CAMBRIAN 
times repeated by folds and faults, with the result of apparently giving 
to them an abnormal thickness. The Linguleila-primeva beds, 
however, form such a clear and definite horizon that on examination 
the cause of this is at once evident. The series indicated by us 
as No. 4 extends to the extreme end of the east point of Porth- 
clais, and it is an entire mistake to show the beds marked by 
Dr. Geikie as his series No. 7 as occupying any part of that point. 
The only other matter which it is necessary to refer to in this 
area is the evidence supposed to he furnished by a quarry of the 
conglomerates nearly opposite the site of the old mull, to fayour 
the view that contemporaneous volcanic tuffs occur in the Cam- 
brian conglomerates. Whether the volcanic forces had completely 
expended themselves or not, before the conglomerates were de- 
posited, may be an interesting point; but it is virtually of little 
or no importance in regard to the questions at issue. The evidence 
we have to deal with is as to the nature and position of the old floor 
which yielded the Cambrian deposits, which are acknowledged by 
all to have been true marine sediments. That this quarry, however, 
does not furnish the evidence supposed is perfectly clear, for the 
so-called volcanic materials alternating with the conglomerates 
here are, like those referred to in other sections, derivative mate- 
rials from pre-existing volcanic rocks. The heds in this quarry 
dip away from the Dimetian, which occurs immediately behind. 
This area was very carefully surveyed by Prof. Hughes and myself, 
accompanied by a large party of well-trained observers from Cam-_ 
bridge in April of last year, and the conclusions as to the various 
points referred to given in the foregoing remarks are those which 
were arrived at during that time. Since then I have revisited the 
area twice, but mainly to complete the evidence. 
I must here also express my great indebtedness to Prof. Hughes 
and to those gentlemen who accompanied him, for the great care 
and trouble with which the various points were examined into and 
worked out by them, and for the general assistance rendered to me 
by them in my reexamination of the district. 
4, Ogof-llesugn. 
The section to which such very special attention is directed in the 
paper of the Director-General, to prove that the Dimetian has been 
intruded into the Cambrian, occurs at or near the place indicated in 
the Ordnance map as Ogof-llesugn, on the coast to the west of Porth- 
clais. The evidence here, it is stated at p. 278, “completes the 
demonstration that the rock, which can be traced from St. David’s 
to the coast south of Porth-lisky, is an eruptive mass that has been 
intruded into the Cambrian strata.” Instead of the evidence here 
furnishing the complete demonstration of intrusion claimed in the 
above quotation, no more satisfactory evidence to the contrary could 
scarcely be desired or obtained anywhere. The want of recognizing 
the differences between igneous junctions and those produced by the 
influences of faults, foldings, and crushings among the older rocks, 
