ROCKS OF PEMBROKESHIRE. 509 
Il. Corrections In THE MAPS SUGGESTED IN THE PREVIOUS PAPERS. 
The points mainly insisted upon in my previous papers as re- 
quiring correction are the following :— 
1. The patch coloured in the Geological Survey map as intru- 
sive syenite and felstone, extending from the coast to the S.W. of 
St. David’s, under that city and to the N.E., in all about 7 miles 
in length, consists of granitoid rocks, of porphyritic quartz-felsites, 
of fine-grained quartz-felsites (old rhyolites), of hiilleflintas, porcel- 
lanites, and of breccias, and these are of Pre-Cambrian age, and 
therefore cannot possibly be intrusive in the Cambrian rocks as 
indicated on the maps. Moreover, the terms syenite and intrusive 
felstone, I maintained, were petrologically either incorrect or utterly 
inadequate to indicate such diverse rocks, some of which could be 
clearly proved to be of sedimentary origin, and others volcanic ashes 
and breccias, &c. 
2. To the N.E. of this area, near Llanreithan, another patch 
about a mile and a quarter long, also coloured as intrusive in Cam- 
brian strata, was shown to consist of old rhyolites and breccias of 
Pre-Cambrian age. 
3. The so-called granite on the shore to the south of Pointz Castle 
was stated to be made up of quartz-felsites of Pre-Cambrian age ; 
and the great granite patch shown on the map as extending in aN.H. 
direction from near the rocks last referred to, for about five miles, 
was claimed to be composed of granitoid rocks like those to the 8. W. 
of St. David’s, and also, like the latter, to be of Pre-Cambrian age. 
4, The patches coloured as porphyries and felstones intrusive 
in Cambrian and Silurian strata to the south and east of the so-called 
granite patch, and forming the elevated areas of Roch, Trefgarn, and 
Ambleston, with broken lengths extending altogether for from 8 to 
10 miles, were also stated to consist mainly of quartz-felsites (old 
rhyolites), breccias, and halleflintas of Pre-Cambrian age. 
5. Returning to the immediate neighbourhood of St. David’s, it 
will be observed that the differences between my views and those 
indicated on the Survey maps are very marked. The extensive 
area coloured there as altered Cambrian, to the W. and N.W. of 
St. David’s, was stated by me to contain rocks totally unlike those 
which had been in this district and elsewhere classed as Cambrian ; 
and evidence was given to show that the latter rested unconform- 
ably on the rocks called altered Cambrian, hence proving that it was 
necessary to class the latter as of Pre- Cambrian age. 
6. I pointed out also that the long patch of so-called intrusive 
greenstone in the Survey map, extending in a N.H. direction from 
Ramsey Sound, consisted mainly of acid breccias, but with a few 
basic dykes, sheets, and ashes; and that other patches of so-called 
intrusive greenstone in the southern portion and making up nearly 
two thirds of Ramsey Island, instead of being basic rocks at all, 
were composed of acid types of rocks, mainly porphyvritic quartz- 
felsites, old rhyolites, breccias, &e. 
The above views, if correct, would necessarily change nearly the 
Q. Ji. G. 8. No. 159. ou 
