Geoscience Reference
In-Depth Information
Landscape E: The Severn Vale
This Landscape consists of the flat areas lying between the hills of folded Devonian
and Carboniferous bedrock of Landscape D and the coast of the Severn Estuary, north
of Avonmouth. Locally, these flat areas are interrupted by hills underlain by folded an-
cient bedrock typical of the Bristol area. The largest of these is near Berkeley ( e1 ),
where a major bedrock structure of tilted and faulted Carboniferous, Devonian, Siluri-
an and Cambrian bedrock runs northward across the estuary. As in the Bristol Land-
scape ( D ), the older bedrock was folded by the Variscan episode, then covered by
more-or-less flat-lying Triassic New Red Sandstone, which was then covered by Juras-
sic bedrock. These flat-lying strata can be seen below both of the Severn Road Bridges,
at Severn Beach ( e2 ) and Aust ( e3 ).
As explained in greater detail in Area 9, it seems clear that an important episode
in the erosion of the Severn Valley has taken place during the last 500,000 years. The
removal of soft Triassic and Early Jurassic mudstones from the valley floor unearthed
discrete hills made of the folded Carboniferous and earlier bedrock and left patches of
relict Triassic and Early Jurassic rock. During this time, the river channel of the Severn
has moved laterally across its floodplain, widening the floor of the valley and resulting
in the deposition of a surface blanket of even younger river and estuarine sediments.
This Region is bounded to the northwest by the estuary of the River Severn. The
river is notable for its tidal bore , a surge involving several waves up to 3 m in height
that moves upstream in the uppermost tidal reaches of the Severn at high tide. People
now compete to surf the longest upstream distance on the best bores. The largest bores
occur when a particularly high tide is combined with critical values of freshwater in-
flow from the River Severn, atmospheric pressure and wind direction. Predictions and
information on locations from which to observe the bore (such as at Minsterworth,
e4 ) are posted on numerous Severn Bore websites. This is the only location in Britain
where this phenomenon occurs so clearly and so often, and indicates the special nature
of the tidal regime and the shape of the Severn Estuary and Bristol Channel.
Landscape F: The Cotswolds
The Cotswold Hills form the eastern margin of Area 8 and consist of erosion-resistant
oolitic limestone of Middle Jurassic age. These hills were extensively explored and
understood by William Smith (often referred to as 'the Father of English Geology')
between 1794 and 1799. Working as a canal and coal-mine engineer, he was able to
demonstrate clearly for the first time, by careful examination of the landscape, that in-
dividual layers of characteristic appearance and fossil content can be followed from
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