Peter Burgess
New member
I have been looking at my lovely geological map, and I have noticed that of the active swallet caves shown on it (Manor Farm, Longwood/August, GB, Tynings Barrow) three are located very close to the point where the streams run off the Lower Limestone Shale, and onto the Black Rock Limestone. Longwood is the exception. This sink is some three hundred metres south of the boundary, i.e. the stream flows over a significant amount of the Black Rock Limestone before sinking. This led me to thinking along these lines:
The active sink for Longwood used to be located similarly to the others, ie somewhere close to the Bristol Waterworks compound at Lower Farm, or within the farm compound. In order to provide a useful water supply for the farm, at some time in the past, the swallet was deliberately blocked, and the water was artifically diverted and channelled to run on the surface through the farm settlement. It found a new place to sink down the valley, which is where it now sinks, and was probably an active swallet at some earlier time in the cave's development.
It may also be significant that the Charterhouse lead works ran a leat from the top of Longwood Valley round the shoulder of the hill into Velvet Bottom, so the interference with the water flow in Longwood Valley might date from the middle of the nineteenth century when this leat was built (according to Stanton and Clarke in the UBSS 1984 paper "Cornish Miners at Charterhouse-on-Mendip").
Consider also that of the four caves I mentioned, only Longwood has a significant 'upstream' series, running back up the valley.
Has anyone considered this before, and is there evidence underground that in the not too distant past, the upstream series once carried the whole stream from an active swallet, now blocked?
The active sink for Longwood used to be located similarly to the others, ie somewhere close to the Bristol Waterworks compound at Lower Farm, or within the farm compound. In order to provide a useful water supply for the farm, at some time in the past, the swallet was deliberately blocked, and the water was artifically diverted and channelled to run on the surface through the farm settlement. It found a new place to sink down the valley, which is where it now sinks, and was probably an active swallet at some earlier time in the cave's development.
It may also be significant that the Charterhouse lead works ran a leat from the top of Longwood Valley round the shoulder of the hill into Velvet Bottom, so the interference with the water flow in Longwood Valley might date from the middle of the nineteenth century when this leat was built (according to Stanton and Clarke in the UBSS 1984 paper "Cornish Miners at Charterhouse-on-Mendip").
Consider also that of the four caves I mentioned, only Longwood has a significant 'upstream' series, running back up the valley.
Has anyone considered this before, and is there evidence underground that in the not too distant past, the upstream series once carried the whole stream from an active swallet, now blocked?