The structural geomorphology of the Dan yr Ogof caves, Tawe Valley, South Wales.

The thesis is concerned with the Dan yr Ogof Caves located in the Carboniferous Limestone of the north outcrops of the South Wales Coalfield. The caves consist of one major system, called Dan yr Ogof, and one other major cave called Tunnel Cave, as well as a variety of smaller caves and potholes. Despite extensive discoveries in the past ten years large extents of cave passages remain unentered and only minimal progress has been made from the major stream input points. While they at present total over 17 kilometres their ultimate extent is likely to at least double this figure. The caves are shown to be comparatively youthful, having been initiated subsequent to the start of the Pleistocene Period, but show a maturity of form which is largely attributable to their favourable geological setting and to the recent climatic history of the area in which they are located. The latter is also held to account for the variety within the three main north-south limbs, for rejuvenation and intensive back-cutting by the River Haffes has been responsible for river capture and the termination of main stream flow into the eastern-most of the limbs. Jointing and faulting are shown to be of very great importance to the orientation and structure of passages throughout the catchment area. However, a hitherto unrecognised syncline is shown to be of major importance in controlling the trend of the most southerly passages which form the main conduit between the bottom end of the north-south feeder limbs and the resurgence. This syncline is the outermost manifestation of a major structural disturbance lying to the south. The large number of faults identified in the cave has led to a detailed consideration of relationships with the surface and it is suggested that an extensive and complex network of faults exists. These are arranged en echelon and are for the most part sub-parallel and trending slightly east of north. A considerable quantity and variety of sediments exists within the caves and some observations are made concerning the origins and chronology of these deposits although it is recommended that they are subjected to specialist investigation at a subsequent date.