The development of thought in Pleistocene and Palaeolithic studies as it affected work in the Mendip area in the period 1919-1969 is briefly traced and the way in which recent developments in the fields of Pleistocene stratigraphy and chronology threatens conventional accepted schemes is discussed. Some implications for the Palaeolithic archaeology of the area are also noted.

A description is given with surveys of the Hepste River Caves. They are four in number and they interconnect: Ogof Afon Hepste, Ogof Tarddiant Hepste, Ogof Tram Trucks and the hepste Resurgence itself. The Hepste River normally sinks four kilometres upstream of this and the water runs underground to both the Western Streamway and the Main Streamway of Ogaf Afon Hepste. The course between the Main Streamway and the Resurgence is lost but the Western Streamway runs through Ogof Tarddiant Hepste to the Resurgence. The uplands of the Hepste - Mellte area contain a number of caves with peculiar features: five are illustrated. The drainage pattern of the uplands is that Pwll Derw goes to the Hepste Resurgence while Ogod Ffynnon goes to the Cwm Porth inlet of Porth yr Ogof. Waterfall Cave in the Cwm Porth Woods does not run to Ogof Glan Mellte. Three of the Upper Hepste caves are illustrated: Blaen Hepste Resurgence, Ogof Glan Hepste and Tuck’s Rift. The Hepste Caves are mainly under water. This makes them divers’ caves not cavers’ caves.

During November and December 1977 a quantitative dye tracing programme was carried out on swallets draining into the Carboniferous Limestone above Burrington, on the northern flank of the Blackdown Pericline, Mendip. Results from the Rickford and Langford Resurgences, known to be the only outlets for the swallets, showed that most of the swallet water flowed to Rickford, suggesting a systematic division of swallet water underground. This has been used to propose a new model for the hydrology of the Burrington area, where swallets rapidly converge to a master conduit system, which then bifurcates, sending water to Rickford and Langford. The larger discharge at Rickford Resurgence is due to the eastward extension to Lamb Leer Cavern, taking in a large area of the limestone plateau, providing a source area for percolation water which makes up some 95% of Rickford’s discharge.

The Passage beds, which are commonly exposed in Mendip caves, comprise mechanically weak calcareous shale beds and tough coarse grained limestones (biosparrudites), it is the biosparrudites which have shown preferential erosion. The biosparrudites have an uneven surface with the fossils standing proud of the matrix. There are thus two scales of differential erosion, firstly between the shale and the coarse grained limestone beds and secondly within the coarse limestone bed, between fossils and matrix. Chemical and microscopic work show that the former is attributed to differences in composition and the latter is primarily controlled by the texture of the limestone. For biosparrudites it is invalid to relate the dissolution rate of the components to the rate of erosion of the whole rock.

A description and survey is given of the Long Gallery in Upper Poulnagollum, from its swallet entrances to its junction with Short Gallery. The authors discuss the effect of differential solution of the limestone beds on the shape of the cave passage.