Dirtlow Rake quarry; phreatic tube in cross section

This photo shows part of the modern open quarrying for fluorite and barytes along the line of Dirtlow Rake near Castleton, on the site of the former Hollandtwine Mine. This is a rather special place. On the far north-west wall, the quarrying has cut a perfect cross section through a cave system. There are vein cavities with horizontal fluting. These lead down to a meandering horizontal passage about 20 m below the original ground level. This passage must have been a phreatic tube at one time - entirely below the water table. The scalloping seen in this photo is a typical solution feature seen in these sort of tubes.

Finally, there is a lot of fine yellow-ochrous loose sediment infilling some of the swallets and partially choking up the phreatic tube. This infill can be seen in the lower part of the photo. I think this is a loess deposit - a fine wind-blown dust originating from rock 'flour' ground up by ice-age glaciers. In the last glacial period (the Devensian) the Peak District was largely free of ice, although it was under cold, permafrost conditions. Strong winds around the periphery of the ice sheets blew all the dust around which accumulated in pre-existing hollows and fissures on the formerly glaciated surface.

So, this quarry has enabled us to see karst (solution) and periglacial features that would normally only be accesible to cavers. I would hope that some of this quarry face would be preserved, but my understanding is that the whole lot will be backfilled and grassed over, so we will end up with a tidy, bland, green grassy area which tells us nothing at all. :-( But I suppose it will keep the planning authorites happy.