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Geology
This version of the essay on geology is from Jonathan Otley's
Descriptive Guide to the English Lakes, 1823, 8th edn 1849. The
copy used is in the Armitt Library, item AMATL:A1180.
It is amended from the essay in the 1st edn 1823, to
accomodate advances in geological understanding.
I am grateful to Tim Pettigrew for his comments on the
essay.
The Latest Geology
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introduction
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Jonathan Otley recognised the broad tripartite nature of the
rocks in The Lakes, each characterised by a distinct
topography.
The earliest rocks consist of slates of a soft character
giving rise to the more rounded fells of Skiddaw and Grassmoor in
the north west of the area. These Skiddaw Slates are now known to
be of early Ordovician age.
The second group he described form the craggy volcanic peaks
of the central area of The Lakes. These Borrowdale Volcanic rocks
are now interpretted as the remnants of a volcanic chain erupting
partly underwater and partly into the open air. Later than the
Skiddaw Slates, these rocks are also believed to be of the early
Ordovician age.
The third group includes the Coniston Limestone, late
Ordovician, and the Brathay Flags which Jonathan Otley correctly,
in the 8th edn 1849, interprets as belonging to the early
Silurian age. The Silurian system had been described by Adam
Sedgwick; he had talked with Jonathan Otley who was able to
incorporate the ideas in his notes.
The 1849 essay predates the recognition of the Ordovician
period, which was defined by Charles Lapworth, 1879. This
introduction to geological theory resolved a dispute between Adam
Sedgwick and Roderick Murchison, who were allocating the same
beds of rocks in north Wales to the Cambrian and Silurian
respectiveley. Charles Lapworth recognised that the fossils in
the disputed beds were different from those in either the
Cambrian or Silurian, and should be in an intermediate period of
their own.
Jonathan Otley describes various igneous rocks, Skiddaw
Granite etc, which were thought to lie beneath and be older than
the rocks above and around them. These are now known to have been
intruded, in a molten or part molten state, into the overlying
rocks which already existed.
A new theory of glacial erratics is mentioned, but Jonathan
Otley still has his doubts about glaciers, and prefers to ascribe
the position of the erratics to the action of water. The coming
of railways is noticed in remarks on the transport of slates from
quarries to the coast.
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Page 144:-
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geology
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THE GEOLOGY OF THE LAKE DISTRICT.
WHEN this essay was first published, in 1820, the structure of
the mountainous district of Cumberland, Westmorland, and
Lancashire, was but little understood; scientific travellers had
contented themselves with procuring specimens of the different
rocks, without taking time to become acquainted with their
relative position. Since that time, the subject has received more
attention from persons conversant with geological inquiries;
especially from the distinguished Professor Sedgwick, who in 1824
and following years, subjected this district to his untiring
examination. In his address to the Geological Society, Feb. 18th,
1831, the Rev. Professor deigned to compliment the author, as
being the first to point out that 'the greater part of the
central region of the Lake Mountains is occupied by three
distinct groups of stratified rock of a slaty texture.'
On a cursory glance at the lake mountains, they present little of
that regularity in appearance which is usually observed in a
stratified country; yet, on a nearer inspection, the
stratification may in many places be distinctly made out; and the
following remarks are offered to the notice of such as require
only a general outline
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