The Peninsula Emerges - Gower - page 28

Increasing numbers of plants were also appearing on the land at this time and they were growing bigger
and more complex than the first terrestrial plants.

TABLE 1. Rock types exposed in Gower, related to simplified geological time divisions. Age in millions
of years before present. (Adapted from Aldhouse-Green, 2000)

AGE ( BP )

PERIOD ROCKS PRESENT IN GOWER

Quaternary 1.8-0 Various glacial and postglacial drift de-

posits

Neogene 23-1.8

Paleogene 65-23

Cretaceous 142-65

Jurassic 206-142 (Found offshore on seabed to the south)

Triassic 248-206 Remnant terrestrial deposits near Port-

Eynon and rare fissure-fills within older
rocks

Permian 290-248

Carboniferous 354-290 Coal Measures in northeast Gower; Mill-

stone Grit; Carboniferous Limestone

Devonian 417-354 Old Red Sandstone

Silurian 443-417

Ordovician 495-443

Cambrian 545-495

The tough, coarse sandstones and even coarser conglomerates form the high ground of Cefn Bryn,
Llanmadoc Hill and Rhossili Down. Since it is only in the cores of major anticlines that these rocks are
brought to the surface all the hills on the peninsula coincide with upfolds in the rocks underneath. Al-
thoughitisnotageneralgeologicalrule,inGoweranticlinesalwaysformhillsandsynclinesalwaysform
valleys. This results from the fact that the older rocks are hard and the younger rocks are soft.
Around 360 million years ago at the beginning of the Carboniferous period there was a major rise in
sea level, which covered almost all of what is now Wales, and the wide coastal plains of the Devonian
landscape weredrowned.Afteraninitial periodwhenmainly muddysediments weredeposited, thewater
became clearer, the amount of detritus reaching the area from the land reduced and limestones began to
form. What is now Gower was then passing across the equator. Even today it is principally in such equat-
orial regions, where there is little sediment being deposited from the land, that limestone is formed. Inthe
warm water lime (calcium carbonate) can be precipitated, and accumulates together with the remains of
marine animals that secrete shells and skeletons. Without the sediment from the land to dilute them, these
shells can form rocks on their own, although many limestones are composed of microscopic particles of
lime, known as lime mud.
The Carboniferous Limestone in Gower is approximately 800 metres thick, with fine exposures in the
southern cliffs, but northwards the sequence becomes gradually thinner and there may also be some parts
missing. This suggests that the sea further north, as it was nearer the land, was shallower. The limestone
consistsofmanydifferenttypes,eachwithadifferenttexture,thicknessandgroupoffossils.Recentstud-
ies have shown that the deposition was controlled by a worldwide rise or fall in the sea level and not by a
local or regional subsidence or elevation of the land. There were several advances and retreats of the sea