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8276823 
Journal Article 
The formation of black deposits in some caves of south east Wales 
Gascoine, W 
1982 
9 
3 
165-175 
English 
Water tracing done over recent years has shown that streams sinking on the surface of Mynydd Llangynidr do not always enter the cave systems beneath at points close to the position of the sinks; indeed in some cases streams flow considerable distances in the upper strata before entering the caves in the lower limestones, and some remain in the upper strata to their resurgence points. Black deposits are often present on the roofs, walls and floors of caves where such streams enter the systems; analysis has shown them to be largely iron and manganese oxides in a carbonate encrustation containing fine sand and some clay. -from Author