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114 slumping or faulting. The choice between these two is not important stratigraphically (although very important economically + structurally) but the evidence is briefly as follows: For faulting: 1. This is a large topographic feature not on the scale of most slumps. 2. The down thrown beds remain for the most part horizontal and without marked dislocation within themselves along a long front. 3. Minor faults parallel (roughly) to this and with a throw of up to 50' are seen. (But they could, less probably, be due to slumping). The throw along the main fault zone would have to be 150', more or less. 4. The uniformity of the phenomenon + coherence of the rather incompetent tuffs speaks against slumping. 5. The base of the downthrust part rests normally on the clays with no slumping surface or zone visible. For slumping: 1. The thick plastic clays beneaththe tuffs form ideal conditions for slumping. 2. Slumping has clearly occurred at numerous points along the outer margin of the downthrust block (but on a much smaller scale and with obvious disarrangement of the beds). 3. The movement is related to the present topography as in a slump, (but if a fault it must have occurred within the present erosion cycle and the valley edge may have been defined by it) and ranging (?) parallel to the valley wall beyond this area. 354 115 355 356 IN BOOK 357 TWO 358 359 360 361 362