By the employment of suitable sampling and analytical methods a marked degree of vertical variability is shown to exist in two exposures of Oxford Clay. Very little of this variation was apparent on visual examination of the strata. Some lateral variation exists between the two exposures, which are thirty miles apart, but this is on a relatively minor scale.

Trends for the vertical variation have been determined and these are in the main common to both areas. The lowest beds are high in organic content and low in acid-soluble lime, whilst higher up in the succession the amount of organic material diminishes and the percentage of lime increases. When examined in greater detail these trends are found to be more complex: they are the resultant of innumerable small scale sedimentary cycles. Thermal methods of analysis have shown that the organic material present in the lowest sixty feet or thereabouts of the Buckinghamshire succession, differs considerably in its ignition range from that found in the next twenty feet. In some respects the characteristics of the higher-level combustible resemble those of lignite. D.t.a. examination suggests that the clay mineral illite is dominant in all layers of the succession in Buckinghamshire. Some montmorillonite may be present in certain of the higher zones either as a simple impurity or in the form of an interlayering with the illite.

The effects of some aspects of these variations on the processes of Fletton brickmaking are discussed.

Study of “tierras de Lebrija” by chemical, dehydration curves, d.t.a., X-ray and electron microscopic methods indicates the composition of these Pliocene sediments to be approximately equal quantities of attapulgite and illite.

Constructional details of the balance and methods to give maximum sensitivity in obtaining and presenting results are described. Examples of work on clay minerals include comparison of results from the balance with d.t.a. traces of kaolinite and halloysite, low temperature dehydration of various montmorillonites, and a series at different rates of heating showing the relation between the d.t.a. trace and the equilibrium isobaric dehydration curve of Li+-Wyoming bentonite.

The thermal dehydration of a series of smectites has been investigated by X-ray methods. It has been found that the rate of collapse of the layers is governed by the type of exchangeable ion present.

The high temperature changes of a new saponite have been investigated. The saponite dehydrates to talc and then to enstatite, the 5·2Å fibre axis remaining constant throughout.

The clay mineralogy of the soils developed on glacial till derived from Carboniferous igneous and sedimentary rocks, and from sediments of Downtonian, Old Red Sandstone and Permian ages is compared with that of the parent rock. The results show that a definite relationship exists between the different soil types developed on the till from each parent rock, particularly in the case of the sediments. The influence of pedogenic processes on the clay mineral distributions in the soil profiles is discussed.

The crystal-chemical basis of the relationship between hydrated calcium silicate and clay minerals is discussed, and a review is given of recent work on the tobermorite minerals, the group of hydrated calcium silicates which most nearly resembles the clay minerals. New data are presented for the specific gravities, refractive indices, basal spacings, and dehydration isobars of synthetic tobermorite minerals, and a tentative explanation is proposed for the variability of Ca : Si ratio in these substances.