Some thoughts on Martin Roe's useful offer of the Victoria Level at
Old Gang in Swaledale as being redriven because the original
gradient was much too steep owing to a surveying error.
As a mining surveyor I must at least try to defend earlier (mid
C19th) practioners of the black art. To accept that it was a
surveying error (even if broadly contemporary writers say it was) is
to overlook the problems faced when setting on a new level. At
Victoria Level, the miners were trying to reach the vein near the
bottom (or just below) the Main Limestone, but how accurately did
they know that bed's vertical position at the intended point of
intersection?
It is comparatively easy to drive a level to meet an accessible point
in existing workings. This is what appears to have happened at
Rampgill Level, at Nenthead. As Fairbairn says (British Mining
No.47) "The original Low Level was driven from near the Nent and
was of small dimension, probably mainly intended as a drainage
level. Mr Dodd, agent for the London Lead Company, decided to
start the present horse level in about 1800, a little above the
original level, so that there would be sufficient height to tip the ore.
By strictly maintaining his level, he eventually got below the old
level." What became of the old level?
It is, however, much harder to estimate the dip of beds, or the
cumulative effect of the throws of faults etc from a distant point to
an inaccessible one. Was this the problem at Victoria Level?
A similar problem had already arisen at the Old Gang Mine, where
the Bunting and Hard Levels were about 4 fathoms apart vertically
when they met. This too was described as a surveying error, but I
find it hard to believe that when the two levels were driven (the
former was begun about 20 to 25 years after the latter) from
different valleys it was envisaged that they would meet (thirl) as
closely as did the Channel tunnels.
This must have been a common problem for mines in sedimentary
strata, where mineralisation was restricted to fairly thin beds - the
Main (or Great) Limestone was around 70 feet thick and was rarely
mineralised throughout.
Here endeth the defence.
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Mike Gill
President and Recorder of the NORTHERN MINE RESEARCH SOCIETY
Britain's foremost mining history society at:-
http://www.exeter.ac.uk/~RBurt/MinHistNet/NMRS.html
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