Great Geologists | 39
Geological cross-section in the Welsh borderlands from Murchison’s paper introducing the Silurian system in 1835. The “Lower Silurian Rocks”
were the subject of controversy and are now regarded as Ordovician.
Noting their trilobite and brachiopod faunas,
Murchison introduced in 1835 the term
“Silurian” (named after the Silures, a Celtic
tribe indigenous to Wales that had resisted
Roman invasion) for these rocks that lay
above the poorly fossiliferous “Cambrian”
rocks that had been introduced by his
Cambridge-based collaborator, Adam
Sedgwick. This included terms such as
Ludlow Beds and Wenlock Limestone,
terms that are still used today and form the
basis for subdivisions of Silurian time.
In 1839 he published his magnum opus
– “The Silurian System”, later revised and
republished a number of times as “Siluria”.
This assured his fame. It was considered
by Leonard Horner, a President of the
Geological Society of London “so accurate
in its details, that a very competent judge,
who had trod, hammer in hand, over every
part of the region, holds it to be the best
piece of topographical geology in our
language. Thus in 1840 he was invited by
Tsar Nicholas I to carry out field work and
report on the mineral wealth of Russia,
especially the Urals region. This led to
the introduction of the Permian period to
describe the distinctive sediments lying
above the Carboniferous Coal Measures
around the Russian city of Perm. He was
also made Knight Grand Cross of St.
Stanislaus by Tsar Nicholas in return for his
efforts.
By all accounts Murchison was a man
confident in his own abilities, possessing
a desire to be the centre of attention in the
geoscientific world and this led him into
a number of conflicts that characterised
British geology in the middle of the 19th
century.
that warranted a separate stratigraphic
term. Accordingly “Devonian” was
introduced in a joint paper by Sedgwick and
Murchison. But the two collaborators were
to fall out over where the lower limits of
the Silurian should lie.
In the 1830’s Sedgwick had carried
out field work in North Wales and had
recognised a series of mostly poorly
fossiliferous slates above basement. These
he termed “Cambrian”. Working at the
same time in the Welsh Borderlands and
South Wales, Murchison recognised the
fossiliferous limestones and shales below
The first controversy was an understanding
the Old Red Sandstone that he termed
of the stratigraphic position and nature of
“Silurian”, but difficulty emerged as to
the “Grauwackes” present in the county
which period some of the then oldest
of Devon in south-west England that
fossiliferous rocks in Wales called the
lay beneath Carboniferous limestones.
Caradoc Sandstones and Llandeilo Flags
Murchison’s initial position was to
should belong to. In essence, mistakes
claim these for his Silurian System, but
and failure to collaborate meant that the
paleontological evidence suggested
“Upper Cambrian” in North Wales turned
something more akin to Carboniferous
out to correlate with the “Lower Silurian”
strata. This dilemma was eventually
in Mid and South Wales. Murchison thus
resolved through study of sections in
claimed the Upper Cambrian as Silurian (in
Europe, especially in the Rhineland area,
an effort to include the oldest fossil-bearing
that indicated that these rocks represented
rocks in the Silurian), whilst Sedgwick
a correlative with the Old Red Sandstone