, Northern Outcrop - Central (Penwyllt to Penderyn)
map using leaflet map:
The entrance is in the quarry floor and is capped & gated.
A small cave connected to OFD via sump. The entrance passage leads to a what was a short sump, Helen's Horror, but has been a crawl since modification in 2010. Beyond is a junction with a small stream: upstream, Ping Pong Passage leads to a choke, downstream, via a 13 metre pitch, to a Default Chamber with water entering from a perched sump and following narrow streamway to a sump. Upstream is Sand Sump, which has been passed by siphoning it.
First discovered in 1938. Rediscovered and extended by SWCC in 1990 and 1994. DudleyCC reentered the upstream Sand Sump extensions in 2015.
Sump feeds first inlet in Cwm Dwr Jama
SSSI: 0099 Ogof Ffynnon Ddu (Mixed)
Brendan Marris 2008
Keith Edwards 2010
Gary Evans 2020
P.Raynes (1938), copied in SWCC Nl 21
SWCC Newsletter 109
Dudley CC 2015, Sand Sump Extensions
Mendip Exploration Society Jl.III (1938), P.Raynes
Descent 100, pp.38-40, Malcolm Herbert & Helen Langford, Cwm Dwr II: Its rediscovery and exploration