The confirmation of the presence of potassium salts in the Permian evaporites beneath the Whitby district, first found in the D'Arey Exploration Co.'s Eskdale no. 2 (Aislaby) boring (G. M. Lees and A. H. Taitt, 1945), and the discovery by Imperial Chemical Industries in their Eskdale no. 3 (Sleights), no. 4 (Sneaton), and no. 6 (Upgang) borings that these salts exist in workable quality and quantity, has been recorded in a recent historic paper by Dr. A. Fleck (1950). The successful outcome of this boring campaign may well lead to the outstanding development of the present century in economic mineralogy in Britain.

For the cutting of chips from rocks preparatory to thin-slicing, it has been standard practice for many years to use notched soft iron disks, manually armed with diamond powder. The latest machines employing cutting-disks of this type at the Geological Museum were built at the Government Training Centre, Ascot Works, Letchworth, to the design of the late Dr. H. H. Thomas and of Mr. W. Ward of the Centre. These are powered with 0.25 horse-power variable speed direct current motors, giving a maximum disk speed of 280 revolutions per minute. By means of rheostats, control of speed as sensitive as that obtainable with a treadle type of machine (see A. V. Weatherhead) is achieved. The normal speed for cutting is 160 to 180 r.p.m. In cutting a hard rock such as chert, it may be necessary to recharge the disk with diamond several times during the operation. The rock-specimen is held in a steel clamp with hardwood liners, mounted on a swinging arm. The rock is held in contact with the disk by the tension of a spring, or, during delicate work, by the pressure of the hand.

The occurrence of acmitic pyroxenes in the post-Cambrian intrusions of the north-west of Scotland was first noted by Teall (Home and Teall, 1892) who recorded aegirine in two dikes discovered by Gunn in the Coigach district of Ross-shire, and aegirine-augite in the borolanite of the Cnoc-na-Srbine mass. Since then, acmitic pyroxenes have been recorded by Teall (1900) from the Assynt felsites, Shand (1910) from dikes of the border zone of Cnoc-na-Srbine, and Phemister (1926) from the dikes and plutonic rocks of the Loch Ailsh laccolite.

Having undertaken a comprehensive examination, in the field and in the laboratory, of the post-Cambrian sills and dikes of the Assynt district, the writer determined some of the optical constants of the acmitic pyroxenes of these intrusions. Arising from this work the considerable data now available on the acmitic pyroxenes has been reviewed. A chemical analysis has also been carried out, and it is hoped that the information assembled and re-interpreted here may be of some general interest.

In October 1945 Count Taaffe, a brilliant if unorthodox Dublin gemmologist, in the course of examining a motley collection of gemstones, came across a small mauve stone which puzzled him greatly. The stone had the appearance, and most of thc characters, of spinel, but afforded clear evidence of double refraction. As recounted below, this stone was later found to belong to an entirely new mineral species-—the only case hitherto known where a mineral has been first encountered as a faceted gem.

The association of clay minerals with sillimanite near Williamstown, approximately 23 miles north-east of Adelaide, South Australia, has been noted by the writer in earlier papers (Alderman, 1942, 1950). These papers described the occurrence of quartz-sillimanite and quartz-kyanite rocks and gave the evidences which suggest that they were formed metasomatically by alumina-rich fluids at high temperatures. It was also suggested that as the alumina-concentration and temperature of the fluids decreased the metasomatic activity was followed by a period of pegmatitc formation which, in turn, gave way to a hydrothermal stage. Brief reference was made to the conversion of sillimanite to clay by hydrothcrmal agencies.

The rocks of the lower and middle evaporite beds of the Permian, passed through by the D'Arcy Exploration Company's boring in 1938-39 (Lees and Taitt, 1946), have been described in earlier communications (Stewart, 1949, 1951). The present paper deals with the petrography of the upper evaporite bed (3655-3860 feet below surface).

Many Jedburgh-type olivine-basalts of Carboniferous age in Scotland are characterized by a sub-ophitic texture in their groundmass and a flow structure of their lathy felspar phenoerysts. These characteristics have been frequently reported in the writings of Geikie, Flett, Bailey, Tyrrell, MacGregor, and others and are recognized as important textural features. In the main, however, they have been described as independent features and have been regarded as unrelated phenomena. Tyrrell (1909) alone has remarked on parallel felspars enclosed in plates of augite, and since his description appeared at an early date and has been available to subsequent workers, the lack of further examples indicates either that his discovery has been overlooked or that the texture is very rare.

Ejected blocks of piutonic igneous facies have long been known in the trachytic and basaltic tufts of Green Mountain and Middleton Peak on Ascension Island, and a petrographic account of them has been recorded by Professor R. A. Daly in his memoir on the geology of Ascension Island.

During the past twenty years considerable attention has been given to the compositions of the pyroxenes from basic igneous rocks. Hess (1941) reviewed the courses of crystallization of pyroxenes from mafic magmas and drew a trend line for the lime-rich clinopyroxenes. The present investigation was undertaken primarily to determine more closely the trend in the ferroaugite region, for here Hess's trend was based on the analyses of two pyroxenes from the Skaergaard intrusion and both of these are now known to be somewhat unusual types. The Skaergaard intrusion which is a strongly fractionated gabbroic complex is Particularly suitable for this study of the ferroaugites. Fifteen new analyses have been made for this investigation and twenty-three analyses of the pyroxenes from this intrusion are now available. Using nineteen of these, new trend lines have been drawn (fig. 1) for the Skaergaard clinopyroxenes.

A rapid and accurate method of determining the density of a mineral has long been sought for by mineralogists and gemmologists. The hydrostatic method gives a high degreeof accuracy, but has the drawback that each estimation occupies about a quarter of an hour so that if some ten to twenty specimens have to be investigated the time taken will be considerable. The use of heavy fluids is rapid, but for finer distinctions a large number of fluids is required and they tend, either from evaporation or chemical change, to become variable, while the Westphai balance is only reliable for fairly large portions of the mineral. Several attempts therefore have been made to develop a balance which will give a direct reading. Most of these such as the Kratschner balance have been based upon Leonardo da Vinci's principle of the bent lever, but generally have not been sufficiently delicate or accurate for small specimens.

During an analysis by X-ray diffraction techniques of some fine-grained leucite-lamproites from the west Kimberley area of Western Australia the author became interested in the rntile in these rocks. Although rutile had been repeatedly observed under the microscope (1, 2), its presence could not be confirmed using X-ray diffraction methods. At the author's request, Professor R. T. Prider supplied a small amount of the mineral which had been identified as rutile. A study of this mineral showed it to be a new mineral similar to rutile in its optical properties.

In the Geological Survey memoir a dike is recorded cutting the Lewisian gneiss near Achmelvich, north-west of Lochinver, Sutherland. At the time the mapping was carried out no thin section was prepared of the rock, and the dike was presumed to be a continuation of the Canisp porphyry dike which is exposed in the river Inver near Lochinver and farther south-east.

During an investigation of the post-Cambrian sills and dikes of Assynt and the adjoining districts of north-west Scotland, the writer examined the Achmelvich dike in some detail and recognized its affinities with the nepheline-syenites. It is the purpose of the present note to describe the field occurrence and petrography of the dike.

The Middle Lias of Rutland, east Leicestershire, and north-west Northamptonshire was described by Judd in 1875 as comprisingan upper ferruginous member—-the Marlstone Rock Bed-—and a lowerargillaceous division of blue clays, often micaceous or sandy, and carryingbands of 'septaria' and of 'ironstone balls'. In the septaria he recordedthe occurrence of 'specular-iron, zinc-blende and pyrites'.

During the six-inch survey of one-inch New Series sheets 157 (Stam-ford) and 171 (Kettering) together with the adjacent parts of sheets 156(Leicester) and 170 (Market Harborough) a considerable area of thelower argillaceous division was mapped.

The hypersthene-gabbro of Ardnamurchan Point is the earliest of the intrusions of Centre 2 of the Ardnamurchan complex as shown by 5. E. Richey (11, p. 208).I The mass is intruded into domed Jurassic sediments and Tertiary basalt flows (fig. 1). The main part of the intrusion is composed of rather fine-grained gabbro, containing 2-3 % of hypersthene which typically surrounds crystals of olivine. Marginally, however, the gabbro is a quartz-bearing variety, with a micrographic mesostasis. The outer contact is somewhat sinuous due to the fact that the intrusion has only been exposed to a comparatively small depth below its original roof. This same geological accident may account in part for the number of fine-grained, basic, granular masses that are locally abundant within the gabbro.

Flint from the chalk of north-western Europe has long been an ingredient of ceramic 'bodies'. It is still widely used by British pottery manufacturers in glazed tries and in certain types of tableware. Continental manufacturers also have made some use of it.

Flint is more readily converted to cristobalite than are the coarsergrained varieties of quartzose silica. The presence of an adequate amount of cristobalite in the 'body' ensures that, at room-temperature, the glaze-film on the ware shall be under a compressive stress. Thus the development of 'crazing', i.e. of minute tension-fissures in the glaze, tends to be avoided.

In the course of the investigation of the crystal structure of sodiumthyroxine- dl it appeared to be necessary, in order to find the approximate orientation of the molecule, to determine the orientation of the indicatrix and the values of the principal refractive indices.

The crystals are flat and very thin (about 0-03 mm. thickness), and when put on a glass slide they all lie on their (100) face. This suggested the use of the universal stage, but the high birefringence of the crystals prevented it from giving good results. Moreover, as the crystals belong to the triclinic system and have no regular contour, it would have been difficult to refer the indicatrix to the unit cell. The interference figures seen when the crystals lie on a glass slide were mis-oriented, though sufficient to determine the sign of the indicatrix, and no clear interference figures could be seen when the crystals were far from horizontal.

To overcome these difficulties the method which follows was developed, and proved to be very useful for all uniaxial crystals and highly birefringent biaxial crystals, whatever their habit.

There are many basic copper chlorides and sulphates which occur as minerals but have received little recent crystallographic study. Yet copper is a widely distributed element and many of these minerals are the products of corrosion and weathering of bopper and copper ores.

In 1948 we were able to confirm the earlier goniometric work of G. F. Herbert Smith (1906) that paratacamite and atacamite are not identical species (Max H. Hey, 1950) and showed that the two minerals give different X-ray powder patterns. This result was further extended by Clifford Frondel (1950) to a single 'crystal and thermal study of paratacamite, in the course of which he measured the rhombohedral unit-cell dimensions and showed that this mineral can be artificially produced by various methods as well as by the action of salt-water on copper.

It is a well-known method in the measurement of birefringence to utilize a crystal's 'bevelled edge', on which appears a sequence of polarization colours, from that colour representing small relative retardation where the edge is thin, to a higher colour corresponding to the full thickness of the mineral in the microsection. In dolerites these bevelled edges on augites are extremely common and are very apparent between crossed nicols. In ordinary light, however, the majority of them are undiscernible and a grain appears to have uniform thickness over its entire area. The reason for the non-appearance of the bevelled edge in ordinary light is straightforward: the augites have excellent relief, that of the adjacent felspars is low; relief is a surface phenomena and independent of thickness, so that a thin edge of augite overlying felspar has the relief of augite, and the felspar is unnoticed.

The origin of the zeolites and associated minerals in vesicles in lavas is a subject on which there is considerable difference of opinion. In general there are two main views: that they are due to the action of percolating surface waters upon thc original minerals of the rock; or are associated with some stage of the cooling processes, as an after-effect of volcanism.

Chamosite is a commonly occurring hydrous ferrous silicate frequently found in close association with chalybite in marine mudstone deposits, the composition of different beds ranging from almost pure chamosite to pure chalybite. In oolitic ironstones chamosite is found both in the ooliths themselves and also in the groundmass. It occurs as a constituent in shales, as a cementing mineral in sandstones, and is occasionally found in lateritic and other deposits. Mineralogically it is usually regarded as a chlorite, or akin to the chlorites, but evidence has been accumulating which tends to show that some varieties may not be chlorites at all, but are probably closely related to the kaolin group of minerals (Brindley, 1949).