Environmental Engineering Reference
In-Depth Information
dip northwards and become progressively older towards the south. This is not the case, because the struc-
ture of the southern part of the coalfield is much more complex than it appears to be from the outcrop
pattern, and on the southern limb of the syncline there is a series of tight folds. The axes of these folds
lie roughly east-west, like the axis of the coalfield itself, and this shows that the pressure that created
these folds was coming from the south. One of the best places to see the structures formed during these
earth movements is at Bracelet Bay, where a plunging anticlinal fold has been eroded by the sea to create
a gently curving pattern of limestone beds in the wave-cut platform. This fold, known as the Langland
anticline, and associated structures such as faults and veins, can also be seen in the cliffs on the eastern
side of Caswell Bay.
Rocks of the latter part of the Carboniferous period are not present in Gower. Around this time a pro-
longedperiodofupliftanderosion,lastingforsome80millionyears,affectedmuchofwhatisnowWales
and adjacent regions. During this time, through the Permian and well into the Triassic period, the Coal
Measures and older strata were folded into the present coalfield basin.
Life flourished during the Carboniferous and Permian. Crinoids, ammonites, corals and fish diversi-
fied in the seas, while amphibians and reptiles continued their invasion of the land. After more than 100
million years of relative stability, however, the end of the Permian (248 million years ago) saw the largest
extinction event in the earth's history, an event far more devastating than the later and much more famous
Cretaceous extinction, when the dinosaurs died out.Around75percent ofknownspecies ofland animals
and 96 per cent of marine animals disappeared forever, together with early corals and trilobites. Many
causes have been suggested for the Permian extinctions including fluctuations in sea level, a change in
the salinity of the ocean, and volcanic activity. The most important factor, however, seems to have been
climate change.
By the end of the Triassic period Gower lay in northern tropical latitudes and the climate was hot and
semi-arid.TheTriassicwasafreshbeginningforlifeonearthandnewspeciesevolvedtofillthegapsleft
by the Permian extinction, with the first dinosaurs evolving towards the end of this period. Throughout
theTriassic,riversystemsrunningsouthacrosswhatisnowGlamorgandrainedintoalakeorlakeswhose
northern shore lay close to the present Bristol Channel. From about 220 to 210 million years ago a com-
plex of mudstones and evaporates was deposited as a result of the rapid evaporation of these lakes. In
some areas these sediments have penetrated and filled fissures in the Carboniferous Limestone. The lakes
appear to have been surrounded by an arid treeless hinterland, since there are few fossils of plants and
insects. Only one small area and a few infilled fissures near Port-Eynon remain as evidence of a similar
Triassic cover in the peninsula. In the 1690s this 'red ochre' deposit from the age of the early dinosaurs
was discovered by John Lucas of Port-Eynon, who considered it a 'seam or deposit of paint material'.
Lucas 'employed men to dig therefore to the great well being and benefit to himself and to the men and
hepossessedmuchwealth inmoneys,anddidbuyskiffatSwainseyandBristol tobeareyepaintmaterial
away to number of five …' This source of material was exploited for centuries and the skiffs carried it to
Cardiffforsale.AccordingtotheaccountsofthePenriceEstatestheuseofthispaintwastheoriginofthe
Great Western Railway livery of brown and ochre. The 1938 edition of the company magazine recording
that they used 10,000 pounds (4,536 kilograms) of 'levigated raw ochre' a year for their paints.
Marine conditions gradually returned some 210 million years ago, reaching their full extent in the
early Jurassic period. The seas were full of life, including ammonites and marine reptiles such as ich-
thyosaurs and plesiosaurs. During this period the early Jurassic sea surrounded islands of Carboniferous
Limestone, such as Gower, and the Blue Lias Limestone was deposited as muds and lime muds in a re-
latively quiet sea, the beds now covering much of the Vale of Glamorgan. Purer and lighter limestones
originating in shallow water then succeeded the Blue Lias. It has long been claimed that thick layers of
younger Jurassic rocks, plus succeeding deposits from the Cretaceous period, including the chalk, origin-
