In a paper read before the Chemical Society I gave a detailed account of a curious reaction of Manganese salts, and showed that Manganese dioxide resembling pyrolusite could be obtained by the reaction. I have since made many samples, and have obtained nodules so like the natural mineral, that I thought that an account of the method might have some interest for mineralogists. When manganous nitrate is dissolved in strong nitric acid and warmed, and a few chips of potassic chlorate added, there is precipitated in the liquid black oxide of manganese in the form of flat plates which, when very thin, are of a beautiful purple, but when thicker are of a red colour. The whole of the manganese is precipitated in this form, but when the strength of the acid and the temperature are made to vary, the distribution of the plates may be changed.

Rather more than twelve months ago Sir D. Jephson Norreys, Bart., of Mallow Castle, county Cork, directed my attention to a beautiful mineral which had been obtained by a friend and neighbour of his, Miss Cotter, of Rockforest. Through his kindness I was enabled to see the circumstances under which the mineral occurred ; and also to obtain from Rockforest some fine specimens thereof.

The mineral itself is specially characterised by the peculiarity of its lustre, which it possesses in a high degree, producing an aspect of a very unique character. Concerning the kind of lustre, this is somewhat difficult to define.

The number of planes is extremely variable in many crystals. Those of the same substance produced under modified conditions, even when issuing from the same solution, are occasionally very different in this respect. Generally the forms become less complicated and the number of planes diminishes, a certain number Of them definitely disappearing, during the crystal's increase in volume. Such transitory planes are very frequently defective in parallelism.

Two kinds of planes may be distinguished on crystals of any system ; some which are constant, others which may be termed variable; the latter being occasionally wanting, are in other cases very numerous.

The difficulty of devising a natural classification of minerals has been recognized by most mineralogical writers, and up to the present time no very satisfactory arrangement has been generally adopted. In the classification of the animal and vegetable kingdoms, although the systems have greatly varied from time to time, something like uniformity has pretty generally existed ever since Linnaeus proposed his famous system of double nomenclature ; but in mineralogy every writer does that which is right in his own eyes—not because there is no king—but because they are many and mutually antagonistic.

This is a highly vitreous transparent reddish brown mineral, which occurs with quartz and rhodocrosite. Its H. is 3.5, and sp. gr. only 2.49.

When heated in a tube closed at one end it gives off water, but is otherwise unchanged. More strongly heated in platinum forceps it loses colour and very slightly fuses on the edges.

It is brittle, and has a highly conchoidal fracture. When digested with hydrochloric acid, oxide of manganese is dissolved out, and the silica which remains is perfectly colourless.

The chapters of this work purport to be chronicles of the present state of our knowledge of the mineralogy of the northern portion of the kingdom. The geognosy and lithology are treated of to such an extent only as, in the first place, to explain the position of the minerals ; and, in the second, to aid future investigators in their explorations.

In these chapters, in order to do full justice to the work of others, the authority for, and the original discoverer of every locality mentioned, will be quoted, wherever known.

The author, having attempted to visit every known mineral locality to the north of the Forth and Clyde, and having succeeded in this attempt with less than half-a-dozen exceptions, is able in most cases to authenticate, or the opposite, as the case may be, the statements of previous observers.

Some time since Capt. Marshall Hall called our attention to Arolla, in the Pennine Alps, as a locality interesting to mineralogists. I venture, then, to offer you a brief note on one-of its rocks, collected during a visit in the summer of 1875.

At the head of the Combe d' Arolla rises the grand mass of the Mount Colon, a truncate cone of precipitous rock, dominating the glaciers of Vuibez and Arolla, which, after sweeping down from the watershed of the Pennine chain, unite into one stream at its base. The highest point of its snowy cap is 12,264 feet above the sea. In the Swiss geological map the greater part of the mountain is coloured as gabbro, and the same rock forms a small peak near the head of the Otemma glacier on the S.W., and the S.W. flank of the Dents de Bertol to the N.E.

In my address at the Annual Meeting of the Mineralogical Society last year, in Plymouth, I gave an account of a new method of studying the optical properties of minerals, and of determining their indices of refraction. I then showed that an approximate knowledge of these characters would, in many cases, enable us to identify minerals with great confidence, and also would sometimes furnish us with valuable hints as to their general chemical composition. My remarks had reference exclusively to detached specimens of more or less considerable thickness, and I scarcely thought that it would ever be possible to apply this method successfully with comparatively high powers in the case of thin sections of rocks. I feared that certain errors, which appeared to be unavoidable, would then become so great in proportion to the difference in the indices of many of the commoner minerals, that it would be impossible to distinguish them with confidence.

Under the name of Romeite a mineral from Borneo has found its way into many collections. There is, however, little in common between the true romeite of St. Marcel in Piedmont and the so-called romeite of Borneo. Both are hyacinth or honey-yellow with darker portions verging towards clove-brown; both contain antimony ; here all resemblance ends. The easy solubility in acids, and the low specific gravity (under 2.0) of the Borneo mineral at once separate it from romeite; it is, in fact, nothing but a variety of allophane containing a little antimonious oxide. The following analysis may not be without interest; the mineral was selected and purified by mechanical means as far as possible, but still contained a small quantity of gangue, chiefly insoluble silica.

It often happens in mineralogical inquiries that from scarcity of materials, lack of time, or other causes, the important datum of specific gravity is not secured. Now, however, that Sonstadt has shown us how to prepare a nearly colourless and perfectly transparent liquid with a density three times as great as that of water, there will generally be no difficulty in ascertaining the specific gravity of very many rare minerals as to which our knowledge remains imperfect. More than this, two minerals if of different specific gravities (provided one is less than S.G. 3.0), may often be easily separated from one another if they are in fragments of appreciable size. Thus, pieces of quartz with a S.G. of 2.655 float, while fragments of beryl (S.G. 2.691) sink in a solution having S.G.=2.67. A very simple apparatus is required for the purpose. (See fig. 7, Plate. VIII.)

In 1861, I described (Edinburgh New Philosophical Journal, and American Journal of Science) a borate, found with glauber salt in gypsum at this place, as a new mineral, by the name of Cryptomorphite, on account of its amorphous appearance to the naked eye being resolved into one most distinctly crystalline, under the microscope.

The first criticism on the mineral was made by Prof. Geo. J. Brush (Tenth supplement to Dana's Mineralogy), who said, in effect, that it could not be accepted and named as a new and distinct hydrated borate of soda and lime, because there were already too many names in use for minerals, not clearly made out to be distinct, having more or less closely similar composition.