In responding to the kind invitation of the Clay Minerals Group, may I say that my notes are intended to express appreciation by a geologist of the illuminating work of the Group, as well as a plea for many favours to come?

History repeats itself. Forty years ago, when the coarser detrital and authigenic constituents of sediments were first being systematically examined, it became evident that their significance could not be assessed until we knew, in broad outline at least, the characters of the assemblages in all the major stratigraphical divisions. The more finely-grained materials were at that time in the main intractable: their investigation has had to await the development of the now familiar techniques utilized by the Group.

One of the most outstanding contributions to petrogenesis and a continuing basis for petrologic argument is the classic reaction relation first propounded by Bowen (1922, 1928). This pregnant summary of petrogenetic process, included in a reaction series, has received affirmation anew from the more recent approach of crystal chemistry and atomic structure of the minerals emphasizing the concept of continuous and discontinuous reaction (Brammall, 1936). The evidence upon which this reaction relation was initially proposed is essentially twofold, firstly a thorough acquaintance with the regular association of certain minerals, particularly the essential and varietal minerals, in igneous rocks and this stemmed mainly from microscopic study, whereas the second line of evidence comprises the guidance received from laboratory synthesis of mineral aggregates (simplified rocks) from prepared melts.

A series of samples of “metabentonites,” here referred to as K-bentonite, and related limestones were collected from the Upper Black River and Lower Trenton formations of the Ordovician System in Central Pennsylvania. The K-bentonite occurs in yellow and gray beds which range from half an inch to ten inches in width.

X-ray diffraction patterns of the 22 K-bentonite samples are similar to those for illite and have the (060) reflection at 1·50Å indicating that the clay mineral is of the dioctahedral variety. However, the value of the (001) reflection ranges from 10·2 to 10·6Å, suggesting that the material is a mixed layer clay composed of expanded and non-expanded layers of hydrous mica (montmorillonite and illite). This possibility was tested by saturating the clay with H, Ca, Na, K, NH4, and ethylene glycol and noting the effect of the treatment on the position of the (00l) spacings in the X-ray diffraction patterns. Using the curves published by Brown and MacEwan (1950) for the analysis of mixed layer complexes, it was found that approximately 20% of the layers are expanded and 80% are not. This ratio is supported by chemical analyses which show that of the exchangeable cations 20% are calcium, sodium, and magnesium and the remaining 80% is potassium.

Although it has been known empirically for some considerable time that the area under the peak of a thermogram (i.e. the area BCD on Figure 1) is approximately proportional to the amount of reactive constituent in the sample, only some five years ago was a simplified theory accounting for such a relationship proposed. This theory is, however, at best an approximation, and recently Arens has attempted a more rigorous mathematical treatment of some of the problems involved. Some incorrect assumptions and derivations in his treatment unfortunately rather vitiate the final result, and, in view of the wide interest likely to be exhibited in this theory, it is perhaps not out of place to draw attention to the inaccuracies here.

In the course of some studies on the effects of anions on the viscosities of clay suspensions, it was observed that anions such as pyro- and metaphosphate, oxalate and fluoride were much more effective in reducing the viscosity of kaolih suspensions than were chloride and nitrate. There is relatively little information available regarding the specific adsorption of anions by clay minerals; it is known, however, that soils take up considerable quantities of orthophosphate from acid solutions. Whether the active component of the soil, in this respect, is the clay mineral or hydrated iron and aluminium oxides, the adsorbed phosphate may be readily released by shaking the soil with neutral or acid solutions containing fluoride, oxalate, citrate or malonate. In addition, a soil which is normally capable of taking up appreciable quantities of phosphate will not do so if fluoride is present in the phosphate solution. It has been recognized that the ability of this group of anions to form soluble complexes with iron and aluminium is responsible for their effectiveness in this respect.

The arrangement of water molecules in the vicinity of clay mineral surfaces has been the subject of much speculation. Vermiculite offers a promising line of approach to this problem since, in addition to its occurrence in soil-clays, it is available as relatively large flakes which can be studied by single-crystal X-ray diffraction methods. This note reports an as yet incomplete structure analysis of vermiculite. A two-dimensional Fourier synthesis has been carried out and a determination of atomic parameters in the third dimension is in progress. The results obtained so far would appear to justify a preliminary statement.

The (h0l) set of reflexions for a natural Mg-saturated vermiculiet were recorded on two multiple-film packs exposed to MoKα radiation in a Weissenberg camera for 100 hours and 5 hours respectively. Intensities were estimated visually by comparison with a set of standards obtained from the (00·10) reflexion.