As a first-aid in the identification of non-metallic minerals I have for many years made use of specific gravity, which is a character that can be easily and rapidly determined hy the use of heavy liquids. A small, clean fragment of the mineral to be tested is dropped into one or other of a series of tubes containing methylene iodide with various small known Crystals as indicators. Adding benzene from a dropping-bottle, the density of the liquid is quickly brought to that of the mineral. This preliminary determination of the specific gravity gives a useful clue as to the nature of the mineral—what it may or may not be ; and the same fragment can then be used for confirmatory optical and micro-chemical tests.

In their paper on 'The structure of α and β quartz', Sir William Bragg and R. E. Gibbs touch on the question of twinning of quartz, showing how X-ray determination of structure can help to explain the different types of twinning. They only mention, however, twinning with parallel axes and twinning on . It would be interesting to see this extended to the examination of all known laws of twinning of α-and β-quartz. There is, however, still much doubt about the laws of the twinning of quartz. Many varieties of twins have been described, but a number of these are much open to doubt, while some are decidedly nonexistent. G. Friedel has within recent years published valuable papers on the laws of twinning in general, and has made more special application of his theories to the laws of twinning of quartz. It would be interesting to see how far all cases of well-established quartz twins occurring ill nature confirm his results.

The old mine Settlingstones, situated three miles north of Haydon Bridge in the county of Northumberland, was originally worked as a lead mine, but, during the htst fifty years, as the vein has been explored farther west, it has attained far greater importance as the largest and most consistent producer of witherite in the British Isles. The Settlingstones main vein has a direction approximately north-east and southwest, and has been proved for a distance of nearly 1½ miles. The vein has varied in width from 3 feet up to 40 feet, the most productive witherite-bearing portion averaging 10 to 12 feet. The enclosing rocks are sandstones ('whetstones') and shales ('plate') of Carboniferous age, and dolerite (Whin-sil) which here attains a thickness of a little over 21 fathoms.

Willemite is a mineral of comparatively rare occurrence, but it has long been mined in New Jersey as an important, ore of zinc (Zn2Sio4, containing Zn 58.6 %), and it would seem also to be abundant in Rhodesia. In the standard mineralogies of Dana (1892) and Hintze (1889) it is mentioned from only four districts. As there is some confusion in the statement of these few localities, and further as several others have been discovered during recent years, a complete list of localities for this mineral has been compiled from the literature; and some others represented by specimens in the British Museum collection are added, inchding the African occurrences now to be described.