In 1819 Sedgwick was appointed Woodwardian Professor of Geology at Cambridge. Four
years later he made a detailed study of rocks in the Lake District. In 1829 Sedgewick
became President of the Geological Society of London. Charles Darwin studied
geology under Sedgwick, at Cambridge, before departing on the 'Beagle' in 1831 as
project naturalist. The two men corresponded regularly and Darwin sent many geological
specimens back to Sedgwick.
He was also a close friend of Roderick Murchison. They did a joint study of the
rocks of Scotland and, in the early 1830s, they worked together in Wales. Murchison's
work led to his definition of the Silurian System, while Sedgwick coined the term 'Cambrian'
to define the system of rocks he studied in mid-Wales. They gave a joint presentation
of their work in 1835. In 1839 they gave another joint presentation on the rocks in
Devon; a study that defined the 'Devonian System' (410 to 360Mya).
Their work in Wales led to a dispute between Sedgwick and Murchison because Murchison's
Lower Silurian and Sedgwicks Upper Cambrian overlapped. The dispute was finally
resolved in 1879 when geologist Charles Lapworth defined the Ordovician
System, encompassing the disputed time sequence.
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Sedgwick was a great benefactor who never lost contact with the village of his birth.
The year after he died, the people of Dent erected a memorial fountain in honour
of their most famous son.
The first picture above shows the 'George & Dragon' hotel in Dent, a charming village
that still retains its cobbled streets and must be little changed since Sedgwick's time.
The second picture is of the Sedgwick memorial fountain.
The Trail
The Sedgwick Geological Trail has twelve exposures marked by numbered wooden posts.
Sites 1 to 4 show Lower Carboniferous limestone, dating from about 330 million years
ago (Mya) dipping approximately 60 degrees upstream. Site 2 has exposed Coral
and Brachiopods indicating that the beds were deposited in a shallow tropical sea.
At site 3 the limestone beds are separated by thin beds of shale showing that conditions
were not stable. There had been short periods when muddy sediments were deposited.
Site 4 has several deposits of black Chert in the limestone possibly resulting from
silicious gel settling on the sea bed.
Moving westwards between sites 4 and 7 there is evidence of an anticline followed by a
syncline with the beds at site 7 dipping vertically. This is evidence of massive
crumpling of the beds due to earth movements. In Tom Croft cave at site 7 calcite
has crystallised out on the surface (see picture below). This is thought to be
caused by heating of the rock, further evidence of massive earth movement.
Between sites 7 and 10 there is a marked change in rock form. Bedded limestone
has been replaced by Breccia. The rock has been shattered into small pieces by
unimaginable forces. Mineralisation is further evidence of intense heating. The
steep sided, narrow river valley has also become wider and shallower.
At site 10 a fine grained mudstone (Brathay Flags), deposited 425 million years ago
and dipping downstream at 62 degrees, has replaced the limestone. At this site one
can also see an unconformity in which the Brathay flags are overlaid by a red pebble
conclomerate.
Adam Sedgwick was the first person to observe and explain these features.
He attributed them to an enormous upheaval that raised the Lake district hills to
the west by as much as 2.5Km relative to the Dales hills in the east. This is now
known as "The Dent Fault".
Two general pictures of the trail and six pictures of selected exposures are shown below:-
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