In the course of a study of certain cerium minerals, a spectrogram of churchite was taken and it was noticed that the cerium lines were barely visible, whereas the yttrium lines were very strong. We therefore decided to re-investigate this species.

Churchite was originally described by A. H. Church in 1865, and named by C. G. Williams in the same year. The specimens were collected by R. Talling from an unnamed locality in Cornwall. It has only been analysed once, by Church, who showed it to be a hydrated phosphate of rare-earths and lime; his quantitative data have been recalculated and included in table I. Church obtained qualitative reactions for the cerium group of rare-earths, and for cerium itself, but made no attempt to determine the ratio of cerium to yttrium earths; he assumed a mean molecular weight for the rare-earths which would correspond to R2O3 324, essentially a mixture of cerium earths with but little yttria, but did not adduce any evidence for this assumption.

Although detailed experimental investigations have been carried out on the lime, magnesia, and ferrous pyroxenes, relatively little attention has been devoted to synthetic studies of the group involving replacements by ions of higher valencies. In the present study, determinations have been carried out on the limits of solid solution of alumina in pyroxenes in the system CaSiO3-MgSiO3-A12O3. Determinations of the solubility of ferric oxide and titania in diopside were also made.

Pure calcium carbonate, magnesia, silica (crushed and washed rockcrystal), alumina, ferric oxide, and titania were used for the preparation of the mixtures. The constituents in their requisite proportions were fused together four or five times with intervening crushing of the quenched glass. The product was an homogeneous glass free from crystalline material.

For several years now it. has been generally appreciated that plagioclase felspar formed at high temperature differs optically from that formed at lower temperatures. Much of the evidence for this has been provided by the Austrian workers, notably Köhler (1-3), Scholler (4), and Tertsch (5-7), who have prepared revised curves to supplement the universal-stage stereograms of Reichert (which are for use with lowtemperature material). There are a number of interesting petrological points which have not yet been fully investigated. Much work has been done on synthetic material, and it is not clear to what extent the hightemperature forms occur naturally. There may be two distinct and separate types of plagioclase structure, or the two forms may grade into one another. It may be possible to explain the optical anomalies as an order-disorder phenomenon; a more disordered state has been 'frozenin' in those felspars which ha~e formed a.t a high temperature and cooled rapidly.

Towards the end of 1952 mining operations at West Sleekburn colliery, Bedlington, Northumberland, involved the driving of a drift through a 'whin' dike. In the process of doing so an unusual, large cavity was penetrated. When the cavity was first entered, by the manager and under-manager, it was found to be water-free but full of 'gas', which rendered them almost unconscious. Their exploration was therefore delayed until the gas was removed by pumping. Unfortunately no sample of the gas was collected, but it is thought to have been 'fire damp'. After examination the cavity repeatedly filled with gas, leading to a suspicion of a hidden extension to the cavity, under the roadway.

The basic technique for preparing micro-thin rock-sections has altered little since this method of studying rocks was first accepted. Abrasive powders were, and still are, used either on glass or metal plates, the grinding being done entirely by hand. At the present time carborundum is almost universally used as the abrasive. The technique has been speeded up somewhat by the use of horizontal metal laps, and in more recent years the introduction of high-speed diamond-cutting and lapping apparatus has considerably reduced the time involved in making a thin rock-section. But even with this apparatus the process is still long and laborious, and, even more important, the operator must have considerable skill and experience in keeping the specimen whole and of uniform thickness throughout the entire operation.

Specimens of the minerals beryl and löllingite were found by me among material collected in the summer of 1950 and the spring of 1951 for work on the distribution of trace elements in the New Consols mine, Stoke Climsland, Cornwall. Unfortunately, I was unable to collect further material, and in the case of the 1ö11ingite its presence on a specimen was recognized only after the mine had been abandoned and become flooded. This locality for the two minerals seems worthy of record in view of the small number of reported occurrences in Cornwall.

The beryl was found in specimens from a pegmatite vein, approximately 2 feet thick and dipping steeply southwards towards the main granite boss of Kit Hill, which was intersected 222 yards from the engine shaft by a south cross-cut at the 52-fathom level.

The narrow belt of granophyre lying to the west of Blaven in the Isle of Skye showed so admirably the effects of chilling that a series of specimens was collected by one of us (L.R.W.) and found to contain, in the chilled marginal rock, phenoerysts of tridymite, now inverted to quartz. In the Thulean Tertiary igneous province former tridymite is known from certain acid lavas, for example, the Tardree rhyolite (von Lasaulx, 1877) and certain Icelandic liparites (Hawkes, 1916), and from metamorphosed arkoses adjacent to basic igneous intrusions (Harker, 1908, 1932), but it has not previously been noted in the intrusive acid rocks. In addition to phenocrysts of tridymite inverted to quartz, there is present in the groundmass of the unchilled granophyre a second generation of inverted tridymite crystals, surrounded by a final stage of quartz and felspar which has crystallized with normal microgranitic textures. Some of the textural features resemble those of the normal Skye granophyres, while others resemble certain metamorphosed arkoses.