In the first part of this paper it was shown that the acid section of the mica group could be divided into two main series, the potash micas and the lithia micas. The molecular ratio of potash to silica was 1 : 6 and the micas were therefore represented as salts of an acid characterized by this value. The present section contains the result of a similar investigation of the basic micas, especially biotite and phlogopite; here again it will be seen that the grouping K2O. 6SiO2 is present throughout. For comparison of the molecular composition, the analyses of the basic micas have been recalculated in molecular ratios, (Si,Ti)O2 being made equal to 600 according to the method already used for the acid micas.

The twofold division of metamorphic rock-series into (a) Isophysical rock-series and (b) Isochemical rock-series, as proposed by P. Niggli in his paper, 'Die Gesteinsassoziationen und ihre Entstehung', introduces into metamorphic petrology two very useful terms, which will be of service in the metamorphic researches that await the attention of the petrologist.

Among such investigated rock-series one may call to mind the studies on the chloritoid-schists of the St. Gotthard massif," the glaucophaneschist suite of the Bagne valley (Wallis), the calc-silicate series of the Trondhjem region, the contact rocks of the Kristiania and Comrie areas. Of these the last are particularly illustrative of an isophysical rock-series, wherein a chemically wide group of assemblages conforming to the composition of shale-limestone sediments is represented in the free-silica and quartzless hornfelses.

Of the garnet group of minerals, two members only appear to have been synthesized from artificial melts, viz. melanite (L. Michel, 1892) and spessartine (L. Bourgeois, 1883, and A. Gorgeu, 1883); though grossular is once reported by E. S. Shepherd, G. A. Eankin, and F. E. Wright (1909) as being produced by reaction under pressure of calcium orthosilicate and aluminium chloride. In dry melts, pyiope is represented by a cordierite-forsterite-spinel assemblage, but no data are yet available to indicate the dry melt assemblages representing almandine. The home of almandine in sediments is the dynamically metamorphosed pelite, and its widespread regional occurrence in these crystalline schists implies a ready synthesis under the influence of shearing stress.

During an examination of zinc ores I had occasion recently to employ methods for the identification of smithsonite, and was surprised to find how scanty and indefinite are the data of its physical properties as stated in text-books. Most of the smithsonite known occurs either compact or as very small crystals many of which are of a composite nature. In this connexion Dr. L. J. Spencer recently acquired for the British Museum some very fine crystals from the Rhodesia Broken Hill mines, and he suggested that this material would be suitable for a detailed examination. These consist of two specimens obtained in 1921 from Mr. W. E. Harris [B.M. 1921, 769] and in 1923 from Dr. O. L. Brady [B.M. 1923, 619] respectively, and are portions of the same mass. Smithsonite crystals were first described from this locality by Dr. Spencer in 1908, but these crystals were minute and showed only the forms v (201̄) and s (223̄).