More that one type of 'dyke'
The geology map, just to confuse things, shows a basalt dyke orientated east west right across the colliery site. the townhead coal seam is outcropping in the long dyke 'valley'; as is the associated limestone that is quarried elsewhere. There's a line of three boreholes put down along the east side of the depression as well for some reason. The yellow on the map is a drift deposit, alluvium, associated with stream and river channels.
On the other map there are a number of wells and springs in the area too, one of those strata beds must be an aquifer. I think the whole thing is natural, although there does not look to be enough catchment elevation to produce much of a stream, I would guess groundwater is breaking the surface nearby and flowing into there. I know by the time you reach the colliery site there is a bit of a stream, and the colliery pumped into it back in the day, polluting the Aln in consequence.
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