Reviews—The South Wales Coalfield, Milford. 275 
Roch, and consists of keratophyres and other rocks. The remarkable 
beds of the Skomer Series were described by Dr. H. H. Thomas in 
1911 (Quart. Journ. Geol. Soc., vol. Ixvu, p. 175), but further details 
dre given in this memoir. They vary from rhyolites to olivine 
basalts, and are interesting on account of the abundance of rocks rich 
in soda. ‘hey are best developed in Skomer Island, but their 
relationship with other rocks is seen on the adjoining mainland, 
where they are overlain by Upper Llandovery beds, which by a curious 
coincidence also contain contemporaneous volcanic rocks. 
_ Of Silurian rocks, the Lower Llandovery beds are similar to those 
in the eastern region, but not so well developed. The Upper 
Llandovery beds contain the above-mentioned volcanic rocks of 
a basaltic character and showing ‘pillow’ structure. In one locality 
certain beds may be referable to the T'arannon stage, but in parts of 
the area, at any rate, there is a marked overstep at the base of the 
Wenlock. 
A full description of the Wenlock—Ludlow succession is given, and 
it is of importance, inasmuch as these beds have a different facies 
from that of those of the typical Silurian area, being marked by 
much arenaceous material and an absence of important limestone 
bands and of graptolitic shales. The presence of Stricklandinia lirata 
and Pentamerus globosus in Wenlock strata indicates that these forms 
must be regarded as facies-fossils and not as zone-fossils. 
The Old Red Sandstone strata are found on both sides of Milford 
Haven, and are in many respects similar to those of the Haverford- 
west region, being divisible into Lower Old Red Sandstone, consisting 
of conglomerates, sandstones, and marls, and Upper Old Red Sandstone 
(the Skrinkle Sandstones), composed of sandstones, marls, and 
limestones. 
The junction of the Lower Old Red Sandstone with the Silurian 
rocks is seen to the north of the Haven. At St. Ishmael’s and 
Marloes Bay the base of the Old Red conforms with the top of 
the Silurian, as seen at the Red Cliff and near Gateholm. ‘‘ There 
is no reason to think that there is any non-sequence.”’ One might 
have hoped that the important Hurypterus remipes fauna would have 
been discovered here: it may yet be found. 
Particularly interesting is the succession of strata at the top of the 
Upper Devonian rocks. “The Skrinkle Sandstones consist of beds of 
‘continental facies’ interbedded with ‘‘ grey sandstones, mudstones, 
and limestones, with an Upper Devonian fauna (‘marine facies’)’’. 
So far back as 1868 the late J. W. Salter maintained, on account of 
the presence of Curtonotus and other fossils at West Angle Bay, that 
marine beds of Devonian age occurred there (Quart. Journ. Geol. Soc., 
vol. xix, p. 480). The list of fossils given in the present memoir 
fully confirms his conclusion. A further account of these important 
rocks is promised when the Pembroke and Tenby Memoir appears. 
As these beds are succeeded by Carboniferous rocks of the Cleistopora 
zone, it would seem that here at last we have the longed-for evidence 
as to the line of demarcation between the Carboniferous and marine 
Devonian rocks of Britain, with all the light which it will throw 
upon the ‘ Devonian question ’. 
