A number of minerals not before noticed as occurring in Britain have been described, and corroborative analyses thereof have been given, in the papers which I have, from time to time, published in the Transactions of the Royal Society of Edinburgh, and also, though to a smaller extent, in the Mineralogical Magazine.

Those which I now bring forward, have been analysed for the most part for a considerable time; but, as it must of necessity be long before I come to notice them, in their proper place, in my “Geognosy of Scotland,” it is well to announce their occurrence without further delay.

The following substances have, for the most part, passed under the names here assigned to them; but they are themselves either ill-determined, or doubtful species: in some cases the name has been attached to certainly more than one specifically-distinct substance.

From Quiraing in Skye. It occurs in layers of an inch or two in thickness, among the amygdaloids. It is usually of a deep-red colour and has a greasy lustre, but is sometimes earthy and dull.

It falls to pieces in water, and may, by this property, and its uniformly dense structure, be distinguished from the red massive mesolite which sometimes occurs along with it.

A dark-grey, almost black, copper bearing mineral, somewhat resembling Redruthite in general appearance, but of a duller lustre and considerably harder; the hardness being between 5 and 6. In parts a bronze tint and lustre is apparent. The specimen exhibits neither crystals nor crystalline structure, it breaks with a well marked couchoidal fracture. Lustre somewhat resinous; streak shining.

Heated in a glass tube it gives off water, having a strongly marked acid reaction, from the sulphurous acid which is evolved. Before the blowpipe it does not fuse, colours the flame green, and acquires a dull black colour. Treated with strong boiling nitric acid it is rapidly acted upon, a bronze coloured residue being left, the residue when examined under the microscope presents a honey-combed appearance; the walls of the irregular cellular cavities are pale-brown and translucent and apparently composed of quartz; when the powdered mineral is boiled with nitric acid, a white residue of silica is left.

It is a common chemical fact, that when a solution containing an alkaline silicate is acted upon by any reagent capable of separating the silica from the base, the silica is in the majority of cases thrown down in a solid form. The fact of this reaction is all that, as a rule, the chemist would look at: but in addition to the mere chemical fact of the precipitation of the silica, another most important element from the mineralogist's point of view is that of the form in which this precipitate of solid matter appears. This form naturally varies with the various conditions of the experiment, and it is by the study of these varying forms that the authors have sought to elucidate, experimentally , the wondrous and beautiful varieties of structure which are so familiar to us in the endless forms of silica occurring in nature.

It was with considerable reluctance that I felt myself compelled to discard the system of coloration adopted in the Geological Survey Maps; and rids I did only after the strongly expressed opinion of several geologists.

It was not that I have any very intense desire to colour rocks after their natural tints, but I have an aversion to adopting a colour suite which departs markedly therefrom; or one which is in discordance instead of harmony therewith. One friend, a man of great scientific discretion, and himself an artist, writes me that when he looks at a recently published geological Map of Scotland, with its grey Torridon and its red Laurentian, he does not know whether he is standing on his head or his heels.

Since my last communication on Artificial crystals (Min. Mag. No. 19), I have met with some very remarkable crystals formed in a Copper Works Slag which consisted mainly of Cuprous Oxide and Ferric Oxide with a little lime, a product from melting a charge of “copper precipitate.”

The crystals are hexagonal plates, bounded on the edges by the faces of a rhombohedron which roughly measured gives an angle of R : R=86° They arc iron black in color, with a splendent metallic lustre, and contain 50% Ferric Oxide with 45% copper.

Examined under the microscope or even with a strong lens, particles of copper and cuprous oxide are visible in a separate state.