We have told you before about the app called Geoheritage of the Dean, which gives you a choice of 11 walks to explore in the Forest of Dean. Having now sampled one of these with our group walk in June we can confirm that the app is very user friendly, gives a lot of background info about the wider geology of the Forest and gives you all the guidance you need in a set of images to follow on each walk. Of course should you prefer you can still enjoy the walks from the comfort of that armchair!
Our walk called in the app ‘St Briavels’ explored the area to the north of that village.
We started on the relatively flat and open higher level on the western side of the Forest of Dean walking on Carboniferous limestone shales. The key feature was a series of swallow holes, or swallets, taking the drainage from some adjacent mudstones. Although rather hidden by summer foliage some of these swallow holes are quite sizeable, in one case having been used by a local farmer as his personal rubbish dump. Overall clear evidence of the impact of acidic rainwater on the limestone.
Our walk then took us quite steeply downwards into the valley of the Slade Brook. On the walk down we had crossed the boundary with the older Devonian Tintern Sandstone. The valley is where the water flowing within the limestone new resurfaces. The fascinating feature is that this water now redeposits its calcium carbonate load, in so doing, creating the unusual series of pools each of which has a rim of calcium carbonate building up on the mosses to form tufa. The image below captures the result.

Our walk then climbed out of the valley to bring us to the eastern rim of the Wye valley. This is an excellent location to remind ourselves how the Wye has incised itself into the landscape regardless of whether it is crossing hard or soft rocks. During that process there are the remains fo several large meanders abandoned at various levels along the Wye. From our viewpoint, effectively on the top of an old river cliff line, we were looking down on one excellent example below us.
The weather was on our side too!
Jim