The new and remarkable mineral locality known as Rhodesia Broken Hill is situated in North-Western Rhodesia, at a distance of about 300 miles to tile north-east of tile Victoria Falls, and at the present terminus of the Cape to Cairo Railway. The outcrop of lead and zinc ore which occurs here was accidentally discovered in January, 1902, by Mr. T. G. Davey, while he was prospecting the country for copper, Rising out of the flat surrounding country is a series of low hills or kopjes, the largest of them being about 90 feet in height ; and these consist almost entirely of oxidized ore. The surrounding rocks are mainly crystalline limestones with some beds of sandstone, conglomerate, and phyllite.

If a drop of strong solution of potassium bichromate, placed upon a microscope-slide, be observed under the microscope as it crystallizes, and if the drop be sufficiently thin, it will generally be found that the following events take place: The first crystals make their appearance at the edges of the drop and after growing rapidly for a short period as branching fibres, they begin to grow quietly in the form of plates or flattened rods presenting the characteristic form of the crystals of this substance. These crystals continue to grow uniformly, but after a short period, at a distance from the growing crystals, and at some spot where the drop is thin, a fresh crystalline growth starts suddenly from a point, and extends with great rapidity in all directions in the form again of branching needles and fibres.

One of the most important and striking properties of isomorphous substances is their capacity for forming microscopically homogeneous mixed crystals, the physical properties of which are, as Retgers has especially shown, intermediate between the properties of the constituents. With the great majority of isomorphous substances the mixed crystals can be obtained in all proportions, but with others the miscibility is limited.

The first case of restricted miscibility was discovered by Retgers in potassium phosphate (mol. vo1.=58.25) and ammonium phosphate (64.17) crystallizing in the tetragonal system ; he did not determine the exact proportions which each salt can take up of the other, but estimated them to be about 20 per cent. each way.

In ‘Nature’ of May 31, 1906, the senior author gave a preliminary account of a new Vesuvian mineral, which he had found amongst the products of the eruption of April 1906, and for which he proposed tile name chlormanganokalite. It was described as a hydrous chloride of manganese and potassium, occurring as deliquescent crystals apparently rhombohedral in form. A few days later, on June 5, 1906, Professor A. Laeroix described, before the French Academy of Sciences, a Vesuvian mineral which he thought must be identical with chlormanganokalite : he stated it to be an anhydrous chloride of manganese, potassium, and sodium, and he determined the deliquescent crystals to be monoclinic and psehdo-rhombohedral. In a later paper, Professor Lacroix rightly insists upon this identity.

Having had occasion recently to draw the twins of calcite, I noticed the advantage of the twin-axes being all placed in the plane of the paper. The representation of the rhombohedron which results from this condition is so unsatisfactory that, obvious as the idea must have been to all crystal draughtsmen, few, if any, seem to have tested the utility of the projection. I desire to point out a few of its advantages.

The mineral strüverite occurs as a rare accessory constituent of the pegmatite which is found in large detrital masses in the neighbourhood of Craveggia (Val Vigezzo, northern Piedmont), namely on the Piano dei Lavonchi and in other localities on the eastern slope of the mountain across which runs the road from Vasca to the Alp Marco. In this pegmatite Professor G. Spezia in 1882 noted the occurrence of beryl, and two years later Professor G. Strüver that of columbite, a mineral which had not hitherto been found in the Alps. Still later, notices of other rare minerals from the pegmatiie were published by Professor A. Piccini and Professor A. Cossa.