The present paper deals with the somewhat obscure lead aluminium phosphates, of which the following varieties have hitherto been described :—

1. (i) The original plumbogummite, a mineral found at Huelgoat in Brittany, and at Nuissière, Dept. Rhône.

2. (ii) Some varieties of pyromorphite, containing alumina and water as constituents. These pyromorphites occur also at Huelgoat, and are usually quoted in books on Mineralogy as plumbogummite, although Damour, in his original paper on the subject, clearly distinguishes between the true plumbogummite and the aluminous pyromorphites.

3. (iii) The American mineral, bitehcockite, occurring in the Canton Mines, Georgia.

4. (iv) A Cumberland mineral, which for some time was mistaken for zinc silicate, but has recently been shown to be a phosphate of lead and aluminium (Miers, Min. Mag. 1896, XI, 272).

The Little Island of Trinidad, as it is called to distinguish it from the larger island in the West Indies, is situated in the South Atlantic Ocean, about 700 miles off the coast of Brazil, in lat. 20°31' S. and long. 29°19' W.

According to Ross, who in 1839 effeeted a landing on tile N.W. coast, the island is a mass of volcanic matter, the rocks of which it is composed assuming the most extraordinary shapes. The most remarkable of these are the Sugar Loaf Hill on the southern and the Nine-Pin Rock on the north-western coast.

Parts of the State of North Carolina, with adjoining areas in South Carolina and Georgia, have long been known to mineralogists and geologists as among the most interesting of corundum localities; and the researches of the late Dr. Genth, Col. Joseph Willcox, Mr. J. Volney Lewis and many other authors have done much to make clear the mode of occurrence and associations of corundum in this area and in the great eorundiferous belt stretching along the line of the Appalachian crystalline area from Alabama in the south to Maine in the north.

In a recent number of this Magazine (vol XI, 1895, p. 16) augelite was shown to be a definite mineral species, having the chemical composition AlPO4.Al(OH)3, and erystallising in the monosymme{ric system. Owing to its rarity, or perhaps to its similarity in appearance to barytes, it has previously only been described three times in mineralogieal literature, and has been f, mnd at only two localities, namely, Westans in Sweden and Machacamarca in Bolivia. It is therefore of interest to be able to record the mineral from a new locality.

The ruby crystals from the Cowee Valley, Macon County, North Carolina, show a very wide variation in their development. Although many of the crystals are so striated that no crystallographic measurements were possible on the reflecting goniometer, the faces were readily identified by means of the contact goniometer. On some of the crystals the faces were bright and smooth, making them well adapted for measurement on the reflecting goniometer. The following references are to Plate.

In a recent number of this Magazine (1897, XI. p. 192) a paper by me on "The Crystallography of Plagionite" gives the results of goniometric measurements and specific gravity determinations made on crystals of plagionite from Wolfsberg in the Harz; it was also suggested on crystallographic grounds that the mineral from Arnsberg in Westphalia described by Pisani as heteromorphite was identical with plagionite: but as no quantitative chemical analyses were made on the material measured, these results were not altogether satisfactory.

During a recent visit to Cornwall the attention of Professor Lewis was directed by Mr. James Wickctt to some composite crystals of copper pyrites recently found in one of the deep mines in the neighbourhood of Redruth. On the specimens acquired by the Cambridge Museum about thirty crystals show this composite growth, which causes the crystals to resemble ill-developed pentagonal dodecahedra of iron pyrites.

The constitution of beudantite, which is one of the small group oz double sulphates with phosphates or arsenates, has so far not been satisfactorily determined. As will be seen below, the results obtained by several analysts differ so much that it is impossible to deduce any simple formula from them.

Grassmann, in his Memoir, Zur physlschen Krystallographie und geometrischen Combinationslehre, published in 1829, referred a crystal to three face-normals--rays--as axes of reference; the parameters being the edges along the axes of a parallelepiped having for diagonal a definite length of a known normal which is not co-planar with any pair of the axial rays. Any other normal is then represented as the diagonal of a similarly formed parallelepiped having for its edges along the axes lengths which are rational multiples of the parameters. Grassmann gave no formulæ for finding in general the indices of face-normals from measurements of the angles on the crystal; nor for determining the angles from the crystal-elements and indices.

In a description of some British pseudomorphs, published in 1896 (Mineralogical Magazine, XI, p. 272), I mentioned that the sky-blue and lavender-blue mineral sometimes found encrusting the pyromorphite from Roughten Gill is not a zinc carbonate or silicate, as commonly supposed, but is a phosphate of lead and aluminium. Pseudomorphs of this substance after pyromorphite are not rare among Roughten Gill specimens, and these were described in the above mentioned paper as examples of plumboresinite after pyromorphite.

The rock-specimens collected during the Antarctic Expedition of 1839-43 were deposited in the British Museum. A few years ago, in the course of a re-arrangement and registration of the rock-specimens n the Museum, this collection amongst others was examined, and microscopic sections of some of the specimens were prepared. Nothing, however, was published at that time, since it was found that the greater part of the collection had been practically duplicated by the rocks of the Challenger Expedition, which had a year or two previously been deposited in the Museum, and it was felt that mere petrographical descriptions of specimens have but little to recommend them in the absence of geological data as to the mode of occurrence and mutual relations of the rocks in the field.

The occurrence in Bolivia of minerals containing the rare element germanium has been recently noted by Prof. S. L. Penfield. One of these minerals from Potosi, described bv him in 1893, has the chemical composition of the Freiberg argyrodite (the original source of germanium), but was determined to be cubic, and not monosymmetrie, the system to which argyrodite was originally referred. To the supposed new mineral the name eanfieldite was given, but when Weisbach's reexamination showed that the Freiberg argyrodite was possibly ctlbie, the name was transferred by Penfield to another mineral containing germanium, which he described in 1894.

This mineral, which until now has been regarded as a hydrated arsenate of iron, was mentioned as far back as 1790 by Proust and also by other mineralogists about the same time. In 1801 Chenevix (Phil. Trans. 1801, 220) gave an analysis of an arsenate of iron, but it differs very much in composition from pharmacosiderite in that it contained 9 per cent. of copper. Probably it was not a pure specimen of this mineral. Vauquelin also published an analysis of an iron arsenate which was probably pharmacosiderite (Brongniart, Traité de Min., 1807, II. 182), since he describes it as crystallising in cubes.

Florencite was first discovered as a rare constituent of the cinnabar-bearing sands of Tripuhy, near Ouro Preto, Minas Geraes, Brazil. Here it occurred in well-developed crystals (up to ½ cm. in, length), in association with monazite, xenotime and the titano-anti. monates (lewisite and derbylite) previously described. Blowpipe experiments made hy Dr. W. Florence showed that the mineral was a phosphate of the cerium earths, while angular measurements of the crystals and observations of the optical characters suggested its close relationship with hamlinite, the new hydrated phosphate of aluminium, barium and strontium, recently described by Hidden and Penfield.

Take three axes of reference OX, OY, OZ mutually at right angles. A convention must be made as to the positive direction of rotation about any line, and that usually adopted is as follows. A positive rotation about OX rotates OY towards OZ, one about OY rotates OZ towards OX, and one about OZ rotates OX towards OY. To find the positive direction of rotation for any line ON we must suppose ON moved to coincide with one of the axes, say OZ, and then apply the preceding rule.

In the eleventh volume of the Mineralogical Magazine, p. 817, in connection with the occurrence of blödite at the Mayo mines, in the Salt Range, allusion is incidentally made to a potassio-masnesian deposit, which was discovered there by Dr. H. Warth in 1878. It occurred as a lenticular stratum in the ' kallar' (impure rock salt) hand separating the Sujewal and Purwála salt beds. The material was more or less mixed up with the ' kallar' itself, and the deposit appeared to be of very limited extent.

It is now ten years since Sauer first described under the name of riebeckite a new species of blue hornblende in the granite of Socotra.

Since that time its occurrence in the British Isles has been noted in the " felsite " of Mynydd Mawr, N. Wales ; in the " microgranite " of Ailsa Craig, Firth of Clyde; in glacial deposits from the Isle of Man; Moel Tryfaen, N. Wales; Greystones, Co. Wicklow; and Greenore, Carlingford; in granophyre from Meall Dearg, Skye; and in felsite from Middle Eildon, Roxburghshire.

In this paper are recorded the observations made upon four exceptionally good specimens of atacamite in the British Museum, which have been submitted to careful study with tile object of determining the geometrical and physical characters of the mineral with greater accuracy than has hitherto been possible. The axial ratios have been calculated with the utmost refinement, an attempt has been made to determine the crystallographic symmetry by a study of the etched figures, and the values of the principal indices of refraction have for the first time been obtained.