Mineralogical Notes [on River-Gravels of the Oxford District

Abstract

All collected from the brick-works at Wolvercote. The Warp is a yellowish-brown sand with a small amount of yellowish mud, which was easily removed by washing to leave a clean light-brown sand. The sand was concentrated by panning, and separated with bromoform, giving an abundant crop of heavy minerals. Very little mica was seen in the washings, or in the concentrate. Sifting showed the presence of a small percentage of grains too large to pass a 30-mesh sieve. These consisted of quartz, subangular and rounded, ferruginous concretions (limonite?), chert-like fragments and lydian-stone. The minerals present in the lighter portion of the concentrate were quartz, felspar (microcline and orthoclase), and muscovite (scarce). The heavy minerals observed were garnet and zircon (abundant), tourmaline, rutile, staurolite, cyanite, epidote, and andalusite. Magnetite, ilmenite, and leucoxene were abundant. No effervescence was observed on treatment with hydrochloric acid. The River-Silt is a sandy clay, the proportion of clay apparently increasing with the depth from winch the sample is taken. The clay is pale blue, with irregular yellow patches. On being washed and boiled, the clay breaks down into a yellow mud, leaving a light greyish sand which contains a good deal of mica. All the sand passed through a 30-mesh sieve. Concentration by panning and separation with bromoform gave an abundant crop of heavy minerals. The lighter portion contained subangular and rounded quartz, felspars (microcline and orthoclase), muscovite, and a few grains of chert. The heavy minerals observed were garnet and zircon (abundant), tourmaline, rutile, staurolite,