The petrology of the igneous rocks has for the last quarter of a century been established,on a sound quantitative basis, largely as a result of the body of experimental work available on silicate melts. In the field of metamorphism, however, progress has been much less marked, and the difficulties of the laboratory development of stresses comparable with those acting during regional metamorphism must for some time leave our knowledge of the crystalline schists far behind that even of the hornfelses. A quantitative approach, however, is not confined to the experimental side. The introduction of the conceptions of facies and grade raises a new need for exact knowledge of the compositions of the various minerals, both of those constituting the different isophysical assemblages of a given grade, and of the isochemical assemblages representing a given rock under the grade-conditions of the various facies established.

When the slip catalogue of the barytes specimens in the British Museum collection was in the course of preparation, a few observations were made which may be of sufficient importance to place on record.

The lists of localities of the barium minerals, barytes, witherite, alstonite, and barytocalcite, in the collection show that rather more than half of the specimens (573 out of 975) come from the British Isles. Hence it would seem that there is a special concentration of these minerals in this part of the world. Possibly this is fictitious, as the collection cannot be considered to be completely representative.

A mass of iron weighing 130 lb., stated to have been found in 1922 near the village of Piedade do Bagre in Minas Geraes, Brazil, and believed to be meteoric, was submitted by Mr. N. Medawar in January 1929 to the Mineral Department of the British Museum for examination. The following description of the mass fully confirms the supposition of its meteoric origin. Unfortunately, only scanty details are available of the circumstances of the finding of the mass. All the information that Mr. Medawar was able to supply is given in the following short note written by Mr. R. J. Bohrer, with a rough sketch-map of the locality.

The axial system of Bravais, with three co-planar axes at 120°C to one another and a fourth at right angles to them is almost universally adopted for the description of crystals based on the hexagonal prism as unit cell. But it does not seem to have been generally recognized that the use of these axes entails some complications in respect of face- and zone-symbols. These it is the purpose of the present note to consider.