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Photo 1
Poppit Sands: alternation of sandstone and mudstone beds of late
Ordovician (Caradoc) age. The sandstones are turbidites, laid down
in deep water by gravity-driven density currents about 430 million
years ago. Some of the sandstone beds are graded with a basal sections
rich in coarse sand to gravel and locally mudstone clasts. The mudstones
are cleaved and folded following the effects of the Caledonian Orogeny
about 410 million years ago.
Photo 2
Cliffs on the north side of Ceibwr bay showing alternation of lighter
grey sandstone beds and darker mudstone beds. The rocks are folded
into a series of large folds and are locally faulted.
Photo 3
Poppit Sands: Folded Ordovician sandstones and mudstones. The softer
mudstones are cleaved and have folded without fracturing. The harder
sandstones have folded with a more angular form and are locally
fractured.
Photo 4
Poppit Sands: quartz veins cutting through Ordovician cleaved mudstones.
The quartz veins were formed when the deeply buried rock was permeated
by and superheated fluids. On release of pressure quartz crystallised
out of the fluids in tension cracks.
Photo 5
Fossils are rare in the local rocks. Graptolites are used to date
the rocks but these are poorly preserved. Animals that crawled along
the ancient sea bed locally left tracks which are termed “trace
fossils”. This example comes from Ordovician mudstones exposed
on the beach north of Llangranog.
Photo 6
View looking east from Carn Bica on the crest of the Preseli hills.
The crags on the right are Carn Menyn, the site of the stones used
to construct Stonehenge. Foeldrygarn, a hill fort, is on the left
in the distance.
Photo 7
Close up of Carn Menyn. Many of these jointed blocks of dolerite
were transported to Salisbury Plain and used to construct Stonehenge.
There is still a debate whether man or glacial processes transported
the blocks.
Photo 8
River Teifi flowing through the gorge at Cilgerran with the castle
overlooking the gorge side. The lower course of the River Teifi
flows through some narrow gorge sections followed by wider, more
open valleys.
Photo 9
Looking south from the Cardigan Wildlife park one can see the steep
sides of the gorge in which the river flows.
Photo 10
Looking from the same viewpoint as Photo 9 but looking slightly
to the west one can see the sloping sides of the older course of
the river. This old river course is now infilled by up to 50m of
sediment laid down before the last ice sheet covered the valley.
Photo 11
Looking northwest from Trwyn Carreg-ddu (Poppit Sands) at the section
of coast where a raised beach is exposed.
Photo 12
Raised beach along the coast shown in Photo 11. The beach is cut
a metre or two above high water mark, and is overlain by boulder
clay deposited about 18 000 years ago during the last ice age.
Photo 13
Close up of the raised beach. The folded Ordovician mudstone are
truncated by a smooth horizontal surface on which is lies a boulder-rich
beach deposit. Boulder clay overlies the beach deposit. The raised
beach was probably cut during a sea level high stand some 125 000
years ago.
Photo 14
Boulder clay deposited during the last ice age about 18 000 years
ago infills the coastal valley at Mwnt.
Photo 15
Close up of boulder clay at beach level at Mwnt. The clay is full
of clasts ranging in size from sand to boulder grade. Some of these
clasts have been transported within the ice sheet from the floor
of the Irish Sea, North Wales and Southern Scotland. These glacial
erratics are common on the beaches of the area and include a range
of igneous and sedimentary rocks.
Photo 16
Erratic boulder of quartzite –probably from North Wales- resting
on mudstones, at Poppit.
Photo 17
Pebble of Jurassic ironstone- probably from the floor of Cardigan
Bay- picked from the beach at patch.
Photo 18
Sand pit west of Penparc, part of a sand unit that extends southwards
to also include Banc-y-Waren. This sand body and that at Monington
were laid down by deltas in an extensive lake during the early stages
of the retreat of the last ice sheet about 18 to 15 000 years ago.
late.
Photo 19
View looking north from above the Webley Hotel at the Pen yr Ergyd
spit that occupies the mouth of the Teifi estuary. The spit is fed
by the gravel on the foreshore on its seaward side. Waved blowing
from the north move the gravel from the foreshore onto the spit
with is slowly extending southwards and forcing the river channel
towards the western (near) shore. A sailing vessel is stranded on
the outer beach, having missed the river channel on its journey
to sea.
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