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 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.

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.

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.

In mineralogical literature there appears to be a tendency to overestimate the degree of exactness attainable in the chemical analysis of minerals. When it is considered how impossible in the majority of eases it is to obtain absolutely pure material for analysis, and how imperfect even in these days are some of the methods of chemical separation employed, for the determination of a formula any great reliance in the figures to the right of the decimal point in the percentages obtained is scarcely justified in the case of analyses made on small amounts (less than half a gram) of material.

In 1869 the late Dr. Sadebeek gave a brief description of a collection of rocks, accompanied by a map and profiles, made by Dr. W. Sehimper in the neighbourhood of Adowa and Axum, Abyssinia.

In the British Museum is a very similar collection, which was purchased from Dr. Schimper about the same time. As some of these rocks showed points of resemblance to the riebeckite-trachytes of Senafé, recently described by the author, a somewhat more detaBed petrographical examination of the specimens than Dr. Sadebeck was able to afford them appeared to promise something of interest.

While engaged last summer in arranging the Carne collection of minerals acquired for the Cambridge Mineralogical Museum in the early part of 1899, my attention was attracted by a single, colourless, transparent crystal, about 10 mm. long, implanted in a shallow cavity on a specimen of crystallised axinite from the St. Just district of Cornwall. In general appearance the crystal resembled somewhat closely one of selenite of the ordinary habit, and indeed was entered as gypsum in the catalogue of the Carne collection.

The metallic grey minerals which are found in the white saceharoida! dolomite of the Binnenthal have been known ever since the old priest Walpen of Binn and R. yon Ritz began collecting them nearly seventy years ago.

The name "binnite" was first given indiscriminately to the grey metallic minerals; afterwards these were subdivided into "Kugel Binnit" and " Stangen Binnit."