Sulphate of Lime—Gypsum

Shotover Hill in Oxfordshire in particular, and all similar formations where soft Marie and Limestone predominate, also the more clayey formations resembling those of Shepey, Brentford, and even Highgate (which has been exposed by digging the Archway), present the crystallized varieties of Selenite in abundance, and show occasionally specimens that lead to the more solid and fibrous varieties.

The upper specimen is from Oxford, and shows how the crystals cross each other, which they often do, and are heaped in bundles more or less crowded and confused. These crystals are frequently very large, in some places from six to ten inches in diameter. The next specimen is from Highgate: it also shows the nature of the arrowheaded mackle commonly catted French Gypsum, which is sometimes found very distinct and large. The coloured face gives the shape as if done on purpose to explain it.

The lower specimen, from Oxfordshire, is destitute of all the lateral faces, or nearly so: perhaps it may scarcely ever be found without some vestige of those that are shown coloured in the Highgate specimen.

This formation sometimes finishes the congeries of veins in Marie; see the lowest specimen, from Purbeck, the sides of which resemble the striated Gypsum; see tabs. 335 and 336.