Environmental Engineering Reference
In-Depth Information
allycoveredthewholeofWales.Noevidenceoftheseyoungerrocksremains,butitdoesseemlikelythat
the chalk, formed mainly from the remains of microscopic plankton called coccoliths, may have covered
much of the country, with the exception perhaps of small areas of Mid and North Wales. It appears that
this late Cretaceous deposit was removed by erosion shortly after it was formed. No Jurassic or Creta-
ceous rocks remain in Gower today, although Jurassic strata have been found offshore to the south of the
peninsula and they also occur to the east in the Vale of Glamorgan.
THE SHAPE OF GOWER
The general topography of Gower has developed since the beginning of the Tertiary period when Wales
was subjected to a long period of periodic uplift. As a result, around Swansea and in the Vale of Glam-
organ there is a series of stepped, but highly dissected, coastal platforms at 60, 90, 120 and 180 metres,
which are considered to be remnants of marine erosion surfaces, or 'wave-cut platforms'. Like similar
planation surfaces in the uplands they truncate pre-existing geological structures. Remnants of the 180m
surface are represented in Gower by the Old Red Sandstone ridges of Cefn Bryn, Llanmadoc Hill and
RhossiliDown.MuchofthepeninsulaisatalowerlevelandliketheValeofGlamorganextendstoalittle
over 120 metres. This 120m platform is not very clear, but can be seen near Pen-clawdd, Three Crosses
and Clyne Common. The southern cliffs represent the lowest platform, later erosion along fault lines pro-
ducing the dry valleys known locally as 'slades'. The general appearance of the peninsula is therefore a
series of plateaus with occasional hills rising above the surface.
The general shape of the south Gower coast is determined by a number of pitching folds (folds with
tilted axes) in the Carboniferous Limestone that result in anticlinal headlands with cliffs and synclinal
bays with sandy beaches. The anticlines occur at Mumbles Head, Pwlldu Head and Oxwich Point,
while synclines form the major bays of Oxwich and Port-Eynon (Fig. 16). The many smaller bays such
as Limeslade and Bracelet have, in contrast, generally been formed by erosion along faults running
north-south (Table 3).
In some locations on the peninsula displacement of the rocks has occurred along a reverse fault, a
breakintherockwhereonemassofrockhaspushedupoveranother.Suchfaultstendtorunparallelwith
the axis of the folds and are called 'thrusts' in Gower, although this is strictly not the correct use of the
term. One such thrust occurs on Cefn Bryn where it is marked by a hollow on the north side and crest
of the anticline that is followed by the road from Cilibion to Reynoldston. Because both the anticlines
and the thrusts in Gower were formed by pressure from the south they tend to lie parallel to one another.
The peninsula owes much of its shape to geological faults. Professor Neville George, Senior Lecturer in
Geology at the University of Swansea, noted in 1933 that 'Almost every bay, inlet, gully, mere, cave or
sound is eroded along a joint or a fault or a fold or a soft bed.' Faulting has, for instance, resulted in the
small coves and bays at Langland, Caswell, Pwlldu and Limeslade (Fig. 17). Other faults run between
the tidal islands of the Mumbles. Each island is also bisected by a smaller fault. The faults may contain
interrupted iron veins, which indicate incremental openings of the fault or fissure.
