In this paper an attempt is made to state and explain, in a simple manner, the essential features of the phenomena which are seen when plates of pleochroie minerals are examined in ordinary light.

The pleochroie effects exhibited by minerals are usually studied in light of practically normal incidence. For the observation of facial colours, transparent crystals, or, better still, specially orientated cube-shaped pieces of minerals, are examined in ordinary light. In general, by this mode of observation, only facial colours are seen when ordinary light is used, and for the observation of axial colours the incident light must be polarized.

In my previous papers I described and illustrated several examples of the concentrically banded and radiated varieties of cassiterite known as ‘wood-tin’, and stated that one very constant character of this variety was its rather remarkable opacity as compared with ordinary cassiterite, which is indeed somewhat exceptionally transparent considering its (often) deep coloration. I also noted the frequent occurrence of specimens of wood-tin encrusted with more or less distinct crystals of cassiterite, or traversed by fissures filled with such crystals, as indicating successive formation.

On October 22, 1903, a considerable shower of meteoric stones occurred in the neighbourhood of the village of Dokáchi, situated near the mouth of the Ganges, in the Dacca district of Bengal. Seven of these stones, which had been obtained flom natives on the spot by Mr. H. E. Stapleton, M.A, of St. John's College, Oxford, Inspector of Schools in the Dacca district, were recently presented by him to the Oxford Museum.

In the year 1904, two specimens were sent to me by Mr. F. H. Batler for determination, which showed small, colourless, rhombie or oblong tabular crystals on granite. The crystals proved on examination to be the beryllium silicate bertrandite, which forms a new addition to the list Of British mineral species.

This mineral was first described by E. Bertrand in 1880 from the quarry of Petit Port, near Nantes, and it has since been found at other places in the same neighbourhood as well as in the old tin-workings at La Villeder in Morbihan, and near Alençon and Limoges, though always in very small quantity. Outside France it has been found only in the neighbourhood of Pisek in Bohemia ; and, in tile United States, at Stoneham and elsewhere in Maine, Amelia Court House in Virginia, and on Mt. Antero in Colorado.

There are probably few subjects for the study of which models are more indispensable than the theories of crystal structure ; but the provision of any considerable series of such models is costly, and they require, moreover, a large amount of space for storage. Some interchangeable models, which the author has lately had constructed to illustrate the space-lattices and the regular point-systems of Sohncke, and which may be fitted up and taken to pieces as required, have been found so convenient, both for lectures and for private study, that a short description of them may be found useful, although they differ only in details of construction from those suggested by Sohncke.

The mineral phenacite (beryllium ortho-silicate) has not previously been recorded from the British Isles. The following notes contain an account of its characters and mode of occurrence at five distinct localities in Cornwall. The occurrences are described in the order of their discovery.

During the early part of 1905, while examining the Cheesewring Quarry, in company with Mr. F. H. Butler, who on a previous visit had discovered bertrandite at this locality, I paid special attention to the diseovcry, if possible, of any other beryllium minerals. I was fortunate enough, after much searching, to find a specimen showing three small crystals that at once suggested the mineral phenacite ; a surmise which On examination proved correct.

In the south-west coal-field of east Glamorganshire—especially in the Lower Coal Measures–Mr. A. Tait, of Caerphilly, observed last year a white, soft, and pulverulent substance, saponaceous to the touch. A specimen sent to me, examined first and identified by Mr. T. Crook, was found to consist of a congeries of well-defined crystals of kaolinite. The crystals are chiefly basal flakes, hexagonal in outline, and 0.02 to 0.037 mm. in length. Most of them show elongation in one direction, and unequal extension of the thin lamellae composing them.