To add to some of Martin's points plus some additional observations.
"I understand that a plan showing the workings at nearby Tankersley
shows galeries radiating out from the shafts. When some of the shafts in the
Emley / Flockton area were exposed during opencasting in the 1950s it is
reported that similar galleries were seen. This is however only an oral
account and they were not recorded."
The Flockton Thick seam lies a short distance below the Tankersley
ironstone. In the Cawthorne / Flockton opencasts that I believe Martin is
referring to numerous shafts down to the Flockton existed along with the
ironstone bell-pits. The measures (mainly mudstones)within which the
Tankersley ironstone resides would have been stripped away as overburden
during opencasting. Only the coal seams prior to lifting would remain
intact. Roadways in the coal seams would be fairly obvious but probably not
those in the ironstone.
"The shafts seen in the Emley / Flockton area worked the Tankersley
ironstone the same as the shafts at Tankersley and display a similar grid
iron pattern. What is very interesting is the relationship between the depth
of the ironstone and the volume of material
in the shaft mounds. Even very cautious calculations show that the amount of
spoil is probably to great for the simple bell pit model."
It is possible that the weak strata associated with the ironstone
necessitated the removal of large amounts of overlying mudstone (the
dominant rock that form the bell pit mounds).
It is interesting to note that all along the Tankersley outcrop you do have
these very large mounds associated with the "bell pit" operations.
"Similar grid iron patterns are seen on the North York moors at Rudland Rigg
where the thin Jurassic coals have been worked from shafts. Over 600 pits
are laid out in a regular grid-iron pattern some 40 to 60m apart, here the
term “multiple shaft” mining has been applied. The coal is shallow(9-12m)
and it is suggested that it was uneconomical to work from one centralised
pit head and this is why many hundred small rectangular shafts were sunk."
Do the local geological conditions dictate the method? It would be
interesting to compare distance between "bell pits" in aligned grid patterns
relative to the geology of the overlying strata, and depth of seam. How does
this vary nationally? What, for example is the cut off depth for true shaft
mining to take place rather than bell pit type mining? Presumably it
could/would vary from place to place.
In the Wrenthorpe / Carrgate areas of Wakefield where the shallow seams were
scrutinised in detail to identify old coal workings, it was often possible
to identify several phases of coal production by examining shaft
distribution. Could this also apply to bell pit / multiple shaft operations?
One presumes that the 600 shafts at Rudland Rigg would have been sunk over a
considerable period of time - are distribution changes evident there?
Comments?
Rob Vernon
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