Jointing, Aspect and the Orientation of Scarp-Face Dry Valleys, near Ivinghoe, Buckinghamshire

The relationships between the orientations of scarp-face dry valleys, elements in the geological structure (particularly joints) and the aspect of the scarp are examined in respect of the Chiltern escarpment at Ivinghoe. Both joints and dry valleys show preferred orientations which are unlikely to be the result of chance but there is only a very weak correlation between preferred joint and preferred dry-valley directions. Even the most deeply incised valleys cannot be related to the joint pattern in any convincing way. The only relationship detected is between the orientations of the regional strike and dip and those of a few valleys or segments of valleys, including parts of the most deeply incised ones. It appears that, in this area, joints do not determine dry-valley orientations but that in some instances strike faults may do so. The evidence does not support an hypothesis of spring sapping for the origin of the valleys. There is a marked tendency for the dry valleys to run either near-normally down the scarp or obliquely from right to left as the scarp is viewed from below. Linear erosion, probably by niveo-fluvial processes and largely controlled in direction by the slope of the scarp face, is a possible mode of origin for those valleys trending normal to the scarp. The obliquely trending valleys may have been inherited from an earlier valley system. THAT JOINT planes serve as avenues of attack for the process of weathering has long been a matter of general field observation. All standard text books in physical geology and geomorphology make reference to their importance (A. Holmes, 1965, p. I03; B. W. Sparks, I960, p. 33). It has further been suggested that in some instances, notably in granite areas, the distribution and frequency ofjoints are important indirect controls of landform. D. L. Linton (1955) concludes that the selection of a particular mass of rock for survival as a tor, while neighbouring masses are decomposed, is a function of the wider spacing of joints at the site of the tor. R. S. Waters (I957) has argued that, complementarily, the relatively broad valley widenings or basins that feature in the morphology of Dartmoor, are the morphological antitheses of upstanding tor-crowned hills, the consequence of differential lowering where joints are most closely spaced. It is also probable thatjoints may in some circumstances be created by erosion; in particular, pseudo-bedding planes or sheet joints are thought to result from pressure release consequent upon the removal of an overburden by erosion. This would appear to be a situation where joints actively contribute to the fashioning of surface form (C. A. Chapman, 1958; Chapman and R. L. Rioux, 1958) in contrast to their predominantly passive role in the formation of tors. The influence of jointing upon fluvial erosion has seemingly excited much less interest. But in an early statistical study of successive 25-foot (7.6 m) segments along the Rivers Wharfe, Ure, and Derwent and the Newtondale glacial meltwater channel, K. Harrison and A. D. Thackeray (1940) confidently suggested a causal relationship between segments with preferred orientations of 024-o25°, II2-1I6° and 163° true bearing, and joints in the Magnesian Limestone, Millstone Grit and Corallian having preferred orientations of o24°, II5° and I63°, as measured by S. Melmore (I938)

Archaeology · Face (sociological concept · Fault scarp · Geography · Geometry · Mining engineering · Orientation (vector space · Sociology · Geochemistry and Geologic Mapping · Geological Modeling and Analysis · Geology · Hydrocarbon exploration and reservoir analysis · Mathematics · Paleontology

• Scarp-Face Dry Valleys near Wantage, Oxfordshire

  Keith Paterson•Transactions of the Institute of…•1977

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• The Soils and Land use of the District Around Aylesbury and Hemel Hempstead. Memoirs of the Soil Survey of Great Britain.

  R E HUGHES, B W Avery et al.•Journal of Ecology•1967

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• The Soils and Land Use of the District around Aylesbury and Hemel Hempstead

  L F Curtis, B W Avery•Geographical Journal•1965

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• The Problem of Tors

  Lester King, David L Linton•Geographical Journal•1958

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• The Geology of Oxford

  E H, W J Arkell•Geographical Journal•1947

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• Differential Weathering and Erosion on Oldlands

  R S Waters•Geographical Journal•1957

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