The water supply of Oxfordshire, with records of sinkings and borings / by R.H. Tiddeman ... with contributions on rainfall by Hugh Robert Mill ... Pub. by order of the lords commissioners of His Majesty's Treasury.

Tiddeman, R. H. (Richard Hill)

Date:: 1910

Credit: The water supply of Oxfordshire, with records of sinkings and borings / by R.H. Tiddeman ... with contributions on rainfall by Hugh Robert Mill ... Pub. by order of the lords commissioners of His Majesty's Treasury. Source: Wellcome Collection.

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$beds are seen only at Shotover. The last-named are insignificant in area and probably in water-supply, and need not be further referred to. The Kimmeridge Clay was penetrated in a boring at Cuddesdon Theological College, and proved to be 180 feet thick, but at Culham Diocesan College it was only 94 feet thick. It does not exceed 100 feet at Shotover on the western side according to J. Phillips.* The clay contains iron-pyrites and selenite (sulphate of lime) and is likely to impart impurities, though not in harmful quantities, to rain-water flowing over its surface. To the water-seeker it is chiefly valuable as a base throwing out water from pervious beds above, or as a covering to spring-Avater Avhich has found entrance to the Corallian Beds lying beloAv it. The Portland Beds include two divisions :— Portland Stone. Portland Sand. Th is division, as mentioned in the Oxford Memoir,! is only applicable to parts of this district ; a division into Upper and Lower is preferable, for both contain beds of sand, and in some parts the lower beds pass into a loamy clay equivalent to the Hartwell Clay. Shotover Hill extends as a straggling outlier to Garsington and Cuddesdon. At its western end the sections show, according to that memoir (p. 51) :— Portland Beds -i f Sands with hard ferruginous bands, 20 or 30 feet. ] Whitish limestones (fossils). 'Upper { Clays, loam and greenish sands, and ) ^ I rubbly glauconitic limestone ... ) Lydites. Blue and brown clay with lydites and phos- phates in base of clay and top of sands ; 3 to 5 feet. ( Yellow and greenish sands with huge spheroidal \ “ doggers ” or calciferous sandstone ; 20 feet. Lower The total thickness of the Portlandian at Shotover is probably about 100 feet. In the same memoir (pp. 52, 53) Mr. H. H. Thomas shows by several observations on different parts of Shotover that the Portland Stone was originally an oolitic limestone, but that by successive changes from percolating waters, ist. The calcareous matrix has been silicified. 2nd. That iron has subsequently surrounded the grains of oolite. 3rd. That further in some parts the grains themselves are conAxrted into secondary quartz in a matrix of iron- stone, forming in effect a ferruginous grit. He suggests that other so-called ferruginous grits may prove to have had their origin in limestones. * Geology of Oxford, 1871, p. 325. f “ The Geology of the Country around Oxford ” {Mem. Geol. Sxirvey), 1908, p. 50.$