Cromford Sough - Alan Brentnall

Tuesday, 3 November, 2015

Very interesting excursion this evening into Cromford Sough for seven of us. We met at the little "recycling" car park just as the rain started, kitted up and headed up the road to the footpath at the side of Ellie's Cafe. This led us to the round stone wall marking the entrance to the sough itself. The passage starts off quite low, with deep water and quite colourful "snottite" formations, but pretty soon gets bigger, and passes the arched brickwork of the side passage that comes from the overflow of the Cromford Mill Dam. Oddly enough, this major passage isn't shown on the PDMHS survey (Bulletin 13-6). After this, we passed beneath five or six shafts of varying heights, before reaching a junction with a branch level, from which a small gushing stream emanated.

Going forward, we entered the section which is annotated on the survey as "bad air - not entered". We had come prepared for this; I had the DCA Oxygen meter, and Pete had a multi gas meter which recorded oxygen, hydrogen sulphide, carbon monoxide and LEL (lower explosive level, based upon methane). Up to this point, we had been experiencing fresh air, with both meters showing levels of oxygen comparable to surface readings. After 200 metres, we passed an inlet from the left (also not marked on the survey) and after this point the draught was considerably reduced, and the air quality began to deteriorate noticably. After another 100 metres, the oxygen level had dropped to 18.5% and 50 metres further on it fell to 17.8%. another 200 metres further in we encountered some old timbers holding up what may have been a fallen in shaft in the roof, and, as my meter was now reading 15.3% oxygen, we decided that we should retreat.

The air got much fresher once we had got past the inlet, and we decided to explore the branch level. The air through out this particular passage was fine, despite the fact that both ends of the branch close down. Eventually we met the side passage to the "alternative exit" at the Mill Dam, and decided to go out this way. All in all, a very interesting trip into one of the earliest soughs driven with the aid of black powder showing interesting formations, and some very fine fossils where limestone is met.