The Origin and Structure of the Lower Viséan Reef-Knolls of the Clitheroe District, Lancashire

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Abstract
Summary The reef-knolls discussed in particular are Crow Hill, Worsaw, Gerna, Sykes and Twiston, all of which lie on the south-eastern limb of the Clitheroe anticline. It is shown that along the eastern side of Worsaw Hill the reef-limestone accumulated at high angles to the horizontal and at depths varying from sea-level down to 400 feet or more below, on a slope running perpendicular to the present strike of the surrounding beds. Shales and thin-bedded limestones were deposited between the reefs and contemporaneously with them on a sinking sea-floor. The larger knolls are considered to be the exposed parts of reefs which were originally ridge-like and ran parallel to the north-west and south-east fault lines and perpendicular to the later main orogenic axes. Some of the reefs may have been several miles in length, but their width rarely exceeded half a mile. Reef sedimentation was followed by uplift which resulted in erosion along the flanks of the reefs and a deepening of the depressions between them. The succeeding Worst on Shales were thus deposited on an uneven surface which resulted primarily from original irregularities of sedimentation but which was modified by subsequent earth-movement. I. Introduction In 1926, in describing the Lower Carboniferous succession of the Clitheroe-Pendle area, I adduced evidence supporting Tiddeman's theory (1900, and Kendall and Wroot 1924, p. 92) of the origin of the reef.knolls. It was argued that the stratigraphy could only be satisfactorily interpreted on the assumption that the limestone hills lying between the villages of

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