In the soil-clays of the north-west of England there occurs a mineral with a 14 Å basal spacing which resembles vermiculite but differs in important ways. The mineral is generally more abundant in the surface soils than in the lower layers but only in rare cases does it form more than a minor part of the clay fraction. The other minerals present in these clays are almost invariably mica, kaolin, quartz, chlorite and often hydrous iron oxides. In one soil however, from Moses Cocker's Farm, Rivington, Lancashire, the 14 Å mineral forms a major part of the clay fraction of the surface soil. This soil has the laboratory number La 55/4 and will be referred to as such. The mineral also occurs in smaller amounts in the clay fractions of the deeper horizons of this soil and as the surface soil is at least in part derived from the underlying material, two other samples La 55/6 and La 55/9 were also included in the study.

Because chlorite represents the highest order of mineral having a montmorillonite-illite like structure, it has been studied by the d.t.a. technique in water vapour atmospheres at pressures (absolute) in the range 0·001 mm of Hg to 2300 mm of Hg. The range of water vapour pressure makes profound changes in the thermograms, showing the very complex nature of the breakdown of the brucite-like layer which was not anticipated by other tests. The chlorite exotherm at 870°C can be completely suppressed by high pressure water vapour or can be greatly intensified by running in vacuum. The great differences in thermograms cannot be explained by chemical analyses or optical properties.

Although differential thermal analysis can now be used to assess the complete constitution of clays and many ceramic materials the silica minerals present many unusual difficulties. The importance of silica and siliceous materials for refractory purposes, the changes which take place in such materials on firing, and the influence of the constitution on the properties of the final product, necessitate a rapid and reliable method for the identification and estimation of the silica phases. Chemical methods cannot differentiate between the various types. X-ray analysis although useful for identification purposes, cannot as yet be used for estimation of the three phases, when all are present together.

Among early observers of the origin and occurrence of clay minerals were those geologists who described the hyarothermal alteration of felspar in granite to kaolinite and of some basic igneous rocks to fuller's earth. There were speculations into the origin of bauxite and laterite and of the effect of weathering on various rocks and minerals in different climates. Little progressr however, was made until clay minerals could be identified by X-ray diffraction and other methods.

Modern studies (Grim 1953) of the formation of clay minerals begin with Noll's hydrothermal synthesis of montmorillonite (1930), pyrophyllite, kaolinite, and mica (1936); since then, most of the clay minerals have been synthesised from their oxides, though attapulgite and hydrated halloysite have not yet been made in the laboratory. Even to-day not enough experimental observations have been made to allow really convincing phase-rule diagrams of these hydrated systems to be made.

The methods used for identifying clay minerals at Göttingen are passed in review. Stress is laid on the use of several different methods, each one alone being liable to errors. In particular, the optical microscope can be very valuable. The phase contrast method has greatly increased the scope of this instrument, especially for determining small r.i. differences (photographs).

After the last retreat of the corrie glaciers in the Ice Age the Mesozoic deposits lying at the foot of the Tertiary basalt cliffs in the Trotternish peninsula of Skye were subjected to substantial landsliding movements towards the sea. A number of lochs were held up partly by the moraines and partly by reverse slopes caused by the landslides. In a number of these lochs, after a period of partial filling by silt, diatomite has been deposited. Most of the deposits are covered with two to four feet of peat. We may roughly estimate the period of diatomite deposition to have been from about 10,000 to about 2,000 years ago. It is hoped to date the deposit accurately when samples have been examined by pollen analysis.

The phenomenon of thixotropy has often been explained by postulating the formation of a lattice structure from the solid particles of the gel. Such a structure is assumed to arise on standing, and to be destroyed on shaking.

Combined electron micrographs and electron diffraction diagrams of single crystals of hydrated kaolins from Hongkong, North Carolina and Indiana show that they have tubular crystal form, but a structure different from that of halloy-site, or of kaolinite, being two-layer triclinic, with β=83°, α=91·8°. They differ in degree of crystallinity, and show some inter-layer water.

For the routine analysis of soil clay fractions in this laboratory, a camera of the type described by Brindley and Robinson (1946) and by Robinson (1946) has proved very satisfactory. In this camera the clay aggregate is mounted on a flat glass slip which may be set at any desired angle to the incident beam.

Oriented aggregates may be prepared by the evaporation or centrifuging of dilute clay suspensions (Bradley et al 1937, Nagelschmidt 1941, Brown 1953) or by pressure (Mitchell 1953), the dry aggregate in each case being cut up and mounted as required. When using a Brindley-Robinson camera, however, it has been found most satisfactory to deposit the aggregate directly onto the specimen slip by centrifuging.

A suitable centrifuge tube, consisting of a body and base-plug turned out of “Perspex” is shown in the figure. The glass specimen slip fits into a depression of its own shape and size machined in the top of the base.

A new method for the determination of the base exchange capacity of small samples of clay minerals has been described by H. van Olphen (1950, 1951). The method is based on the exchange of the exchangeable cations against large organic cations; for the latter, cetyltrimethyl ammonium bromide (lissolamine) was used. The point of complete exchange can be detected by an emulsification test: at the point of equivalence the clay becomes an excellent emulsifier for oilwater systems; this is supposed to be due to its being at one and the same time oleophilic at the surface and hydrophilic at the edges of the particles. It was considered of interest to study the adsorption of lissolamine on clay, as this would contribute to our understanding of the method.

The Japanese archipelago, in the temperate zone, has been affected by volcanic and hot spring action in many geological periods including the Recent one. Complicated clay mineral assemblages have been formed by alteration of volcanic glass both by weathering and hydrothermally, and have been studied by the writer and his collaborators (Sudo, 1950b, 1951; Sudo, Minato and Nagasawa, 1951; Sudo and Ossaka, 1952). The present account, based on these studies and on more recent data, deals with acidic to intermediate types of volcanic glass, which are widely distributed in rocks and soils throughout the islands.

Sodium montmorillonite and pyridine form a regular complex of spacing 23·3 kX in the presence of traces of moisture. The minimum interlamellar composition necessary for the formation of the complex is approximately Na+ (C5H5N)4 (H2O)2. The intensities of the 00l reflections are considered incompatible with the complex having a five layer structure and an alternative arrangement is proposed.

Kaolin, or china clay, unlike most of the other clays mined in the United Kingdom, is residual in character, not sedimentary, being formed in situ in the mass of granite by decomposition of the original felspar. Granite occurs over a very considerable area of Great Britain but only in the granite bathylith of S.W. England, in Devon and Cornwall, does sufficient kaolinisation occur to justfy extensive exploitation which has been proceeding now for over 180 years. The granite intrusion welled up from great depths under a cover of sedimentary rocks of much greater age, which cover had already undergone great tectonic stresses prior to the granite's arrival.