In 1938–39 the D'Arcy Exploration Company, Limited, sank a borehole (Eskdale well no. 2) to a depth of 5040 feet near Aislaby, Eskdale, Yorkshire, to test the oil or gas possibilities in the Permian Magnesian Limestone. As the well was some distance from any previous boring through the Permian salt series, the Company undertook to carry out continuous coring through this series in the public interest. The boring passed through Lias, Rhaetic, and Trias, and finished in the Permian Lower Magnesian Limestone. The geological results of this boring have been discussed by Lees and Taitt (1945), and fig. 1 has been reproduced from their paper. It can be seen that three evaporite beds were passed through; two in the Upper Permian salt zone, and one in the Middle Permian.

Among the specimens collected at the Benallt manganese mine in 1944 by Dr. A. W. Groves and myself was one (B.M. 1944,48) from the 60-foot level in no. 1 ore-body which showed on a face of dark, compact manganese ore colourless plates up to 7 mm. across and about ½ mm. thick. These plates proved to be uniaxial and negative with perfect basal cleavage. Heated in an ignition tube the fragments decrepirated, gave off water, and became pearly, white, and opaque. Qualitative tests showed Ba, Al, and SiO2 to be present. Preliminary X-ray photographs revealed hexagonal symmetry, but could not be matched with those of any known mineral.

The plagioclase which forms the subject of this investigation was presented by Dr. C. Stansfield Hitchen, director of the Kenya Geological Survey, who has kindly sent the following note of its occurrence:

In previous editions of Hatch's ‘Petrology of the igneous rocks’ including the last two, for the revision of which the writer was largely responsible, historical precedent was followed and the main lines of classification were based on variation in the silica percentage. In preparing for the new post-war edition considerable thought has been given to this matter. The weakness of the scheme has become increasingly apparent to the writer, and it is now obvious that no juggling with the selected ranges of silica percentage chosen to delimit the ‘acid’, ‘intermediate’, and ‘basic’ categories can result in a workable, logical scheme. Silica percentage as a basis of rock classification must be abandoned for the reasons discussed below.

A noticeable feature of many of the soils of north-east Scotland is the presence in them of glistening yellow flakes of decomposed biotite. The light-reflecting property of this material catches the eye even though the flakes themselves are often of very small size.

An analogous process to the breakdown of biotite as reported below occurs in the soil-clays of the area, and the present study was undertaken primarily in order to throw light on the mineralogical nature of the clay fractions of the soils, since the large amounts of anmrphous material associated with the soil-clay minerals renders less satisfactory the direct approach. The mineralogy of the soil-clays will be dealt with in a separate communication.

During soil survey in the Deeside district of Aberdeenshire, a light greenish-yellow clay-like material was observed penetrating and coating the altered rock along a vein in a granite outcrop freshly exposed in road-widening operations one mile north-east of Ballater. The material occurs in a crush-band in the rock, and the alteration is apparently due to the action of water, but since the band was still highly altered at the base of the exposure (about 25 feet from the surface) it is not certain from the field relationships whether the water was of hydrothermal origin or whether it percolated from the surface.

A thin belt of serpentine up to 400 yards wide and about 6 miles long runs SSW. from Portsoy, Banff, and parallel to the general structure lines at that locality. Near Damhead, 1½ miles SSW. of Portsoy, an old quarry has recently been reopened in this belt and worked to a depth of 98 feet for the exploitation of talc. The general association in this quarry, stated in order of quantitative importance, is serpentine, talc, dolomite, the last being present in very minor amount but of an unusual character meriting description. In the following account the particular task of one of us (E. M. P.) has been the preparation of chemical analyses, the other author being responsible for descriptions and discussion.

Mineralogists have long been accustomed to describe hardness with the aid of a scale devised by Friedrich Mohs, who lived from 1773 to 1839. The test is qualitative, each mineral in the scale being capable of scratching those that precede it, but the ten minerals have held their ground as a useful representative series with which it is now interesting to compare another method of estimating hardness.