58 DR T. J. JEHU ON 
The granite covers an area lying immediately to the south of St David’s, and there 
is another wedge-shaped mass a little to the south-west, reaching the coast on the 
eastern side of Porth-lisky. The St David’s mass graduates into a spherulitic quartz- 
porphyry and felsite at its northern end. The granite is surrounded on all sides but the 
south by rocks of the voleanic series which are marked as Andesites on the index-map. 
These form a ridge running H.N.E. and W.S.W., stretching from Llanhowell, past the 
city of St David’s, to reach the coast at the southern end of Ramsay Sound. Two 
detached masses are marked further east, about Llanreithan. 
The volcanic group consists largely of bedded tuffs; but lavas also occur, and give 
rise to prominent crags to the west of St David’s. 
Dykes and sheets of diabase traverse the other formations. 
These igneous rocks are flanked on the west and south-west by the Cambrian 
conglomerate, and this is followed by green, purple, and gray flagey sandstones, with 
intercalated red shales. Towards the base, fragments of Olenellus were found by Dr 
Hicxs. In a south-east direction these are followed by the gray and black flagstones 
and shales of the Menevian series, and these again by gray and bluish flagstones and 
slates of the Lingula Flag series. Still further eastwards, a small tract of Tremadoe 
beds is found near Tremainbir. | 
Beds of the Menevian and Lingula Flag series also occur at the south of White- 
sand Bay. The Lingula flags run as a continuous band from the bay inland as far as 
Crug-las, and on the north a band of Tremadoc flagstones and earthy slates runs parallel 
to a point south of Abereiddy Bay. 
The north coast from St David’s Head to Abereiddy is made up of slates and 
shales and flagstones of Arenig age. Masses of gabbro occur at St David’s Head, and 
a little east of this, diabase masses, giving rise to rugged eminences, are seen. 
North-east of Abereiddy the Llandeilo flags succeed the Arenig series, and consist 
of black slates and flags, sometimes calcareous, and some felspathic tufts. 
Numerous bands of “felspathic trap” are seen to occur in the tract bordering 
Abereiddy Bay. 
Kastwards from the St David’s promontory, right into mid-Wales, the sedimentary 
rocks are marked in one colour on the Survey maps, and are referred to as ‘‘ Lower 
Silurian (including Upper Silurian not yet separated).” They consist of shales, slates, 
and gritty sandstones, with some flagstones. Mr Cowper Rerp found that beds of 
Llandeilo and Bala age form Strumble Head. Immediately around Fishguard we 
meet with Llandeilo and Arenig beds, and further east with Upper Llandeilo and Bala 
beds again. Dinas Island is composed of sandstones, slates, and conglomerates of 
Llandovery age. 
The country around Fishguard is rich in igneous rocks.  Felsites, tuffs, and 
agglomerates contemporaneous with the Llandeilo and Bala beds occur, and intruded 
into these are sills and masses of “ greenstone.” The latter include basalts, dolerites, 
diabases, and gabbros. 
