If the visitor standing at Wherry Town on the south-western end of the esplanade at Penzance looks seaward he will observe at low tide at some distance from the shore a low scaweed-clothed rocky shoal (fig. 1), and from his now very conventional surroundings it is difficult to realize that upon this shoal, always surrounded by water, there existed many years ago a rich tin mine, unique in the boldness of its conception, romantic in the extreme in its situation and execution, and withal the effort of a poor working miner.

Very fortunately in the year 1790, during the hey-day of its career, this remarkable mine was examined by a very competent observer in the person of John Hawkins (1761 ?-1841), F.R.S., of Trewithen, Cornwall, and Bignor Park, Sussex, and it is to him that we owe most of the details concerning its mode of working, &c. The Wherry mine and its history have always fascinated me, as they must have many others, and in re-telling the old story I have endeavoured to collect all the known facts, both as to the mine itself, its mode of working, and its mineral productions, and in so doing pay tribute to its gallant and resourceful originator Thomas Curtis.

Johann Wolfgang von Goetiie (1749-1832), the bicentenary of whose birth at Frankfurt-on-Main will be commemorated on August 28, 1949, gave us extensive accounts of the development of his studies in optics, botany, and meteorology; with regard to the history of his studies in mineralogy and geology, his most concise statement is his essay ‘Geology, in particular that of Bohemia’. This essay, written in 1817, starts with three quotations. The first is in English:

What is the inference ? Only this, that geology partakes of the uncertainty which pervades every other department of science.

The source of this quotation still remains to be discovered. At the end of this essay, Goethe said that he was:

fortunate in obtaining a series of minerals from all the principal countries. Herr Mawe, the mineral merchant in London, provided me with a most satisfactory collection from Cornwall, and to Herr Ritter v. Giesecke I am indebted for an important addition to my collection of English stream tin and Malacca tin. All these materials have now been well arranged in my collection, but my plan to write something conclusive on this subject could not be carried out, as so many other things I should have liked to do in the scientific field.

In an earlier paper the authors described the occurrence of artificial kalsilite in the hearth of no. 3 blast-furnace of the Kettering Iron Company. That paper contained a detailed description of the furnace campaign together with the peculiar conditions observed in the excavated hearth which was found to exhibit zoning in a vertical direction. The third zone containing kalsilitc was described in detail, but the only reference to the second zone stated that it was 2 inches deep (fig. 2, p. 77, this vol.) and consisted of a black glassy slag containing numerous crystals of cordierite (p. 78). The detailed examination of this zone now forms the basis of the present paper.

It is a familiar fact that in dikes, lava-flows, and sills the grain-size of the individual minerals normally varies according to the distance from the contacts. At or near the margins of the igneous body the grainsize is usually very much less than in the centre, and this phenomenon has been attributed to differences in the cooling-velocities at these spots. On the basis of measurements carried out by Queneau (8) the opinion seems to have been formed that the crystal-size always shows a progressive increase from the contacts towards the centre. This is not so, however, for as Lane (6) has shown, the crystal-size may increase to a maximum at a certain distance from the margin, and thereafter decrease again towards the centre of the intrusion. Apart from these investigations, carried out by Queneau and Lane, the only additioual quantitative data oil crystal-size variation known to the writer concerns a series of measurements made on an olivine-diabase by B. H. Dollen, under the direction of H. L. Alling.

The ionic radius of zinc (0·83 Å.) is identical with that of divalent iron (0·83 Å.) and nearly the same as that of magnesium (0·78 Å.). One would therefore expect zinc to be mineralogically closely related to iron and magnesium. It is, however, well known that this is not the case. An examination of a list of the zinc minerals which have so far been described shows that only in a few cases are the corresponding isomorphous ferromagnesian species known. As a rule zinc minerals and iron-magnesium minerals with corresponding chemical formulae are entirely different in their crystal-structure.

The occurrence of dickite in the gold-bearing rocks of the Witwatersrand system was first reported by Mr. H. C. M. Whiteside. In addition, among the many mineral samples given to me by students of the Witwatersrand Technical College, Johannesburg, were several dickite specimens from mines all along the Witwatersrand area. Dickite may therefore be regarded as fairly widespread in the rocks of at least the Main-Bird series, although not in large quantity.

The only occurrence of which a detailed record is available is that from the Daggafontein mine. Little is known of the other samples except from the immediate mineral associations. It is, however, clear that all the occurrences are of hydrothermal origin.

The Egyptian clays under consideration are obtained from two different localities. The Aswan clays are mainly concentrated in the neighbourhood of Aswan town in Upper Egypt and the Sinai kaolins from the Sinai Peninsula. The Aswan clays, namely: red Aswan clay, white Aswan clay, and siliceous Aswan clay, are transported clays, while Aswan kaolin is a residual clay. The Sinai kaolins are of obscure origin but most probably are transported clays. As is shown later, these are alunite-bearing clays not previously recorded in Egypt.

The affinity between certain organic compounds and clays has been known for many years. Lloyd reported the adsorptive capacity of fuller's earth for alkaloids in 1916 without theorizing extensively about the mechanism. Smith reacted organic bases and their salts with bentonite and presented evidence that the reaction was one of base-exchange or metathesis, while Hauser has discovered that certain organic compounds of bentonite have the property of swelling and dispersing in organic liquids. This paper reports observations on the rather striking conversion of bentonite from the hydrophilic to the organophilic condition and proposes a mechanism to explain the observed phenomena.

In his work on the mineralogy of soils colloids G. Nagelschmidt, suggests the possibility of a reversible change of the type

We have attempted to establish experimentally the existence of this transformation following fixation or departure of the potassium from between the fundamental structural sheets of the mica type. The initial material was montmorillonite from Camp Bertaux, Morocco, separated from its impurities by sedimentation. As it was evident a priori that the alteration of montmorillonite into illite necessitates (1) saturation of the base-exchange capacity of the minerals by potassium, and (2) the departure of the layers of water from between the structural sheets of the montmorillonite, we finally, after several attempts, were led to make use of the following technique.

One of the problems which occupy the mineralogist as well as the geologist or pedologist is the mechanism of the formation and evolution of minerals in nature. In this general connexion we have been trying to clarify the possibility of passing from montmorillonite to chloritic minerals. Already in a previous work we showed that on precipitating magnesium with ammonia in the presence of montmorillonite, a substance is obtained which shows certain of the characteristics of vermiculite and chlorite. Having thus shown the possibility of passing from one type to the other, we wished to clarify the mechanism of the change. We wanted to know what are the conditions of the transformation, and then to follow the montmorillonite from the moment when it was in equilibrium with the solution of magnesium chloride to the end of the alteration. Finally, it had to be established to what extent the product obtained resembled or differed from the standard minerals. These different points will be considered in succession.