In modern petrology increasing importance is being attached to the content of minor chemical constituents, the determination of which is now frequently required, whereas hitherto they have usually been disregarded. In consequence, methods for their accurate determination in small amount have not always been fully worked out. Copper is a case in point, and it is already clear that the method here advocated will show that this metal is much more widely distributed in rocks than is generally realized. Moreover, the use of a large sample, such as 20-50 grams, is no longer necessary.

In attempting to apply to rocks the very sensitive colorimetric method described by T. Callan and J. A. Russell Henderson, various difficulties were encountered, and modifications were developed whereby the method can be adapted to the determination of from 0·001-0·25 % of CuO in silicate rocks and minerals. The reagent used is sodium diethyl-dithio-carbamate, which gives a yellow colour with copper in slightly ammoniacal solution. The authors give a list of other metals which also give a coloration or turbidity with this reagent.

Introduction and mode of occurrence.-During a visit in 1929 to the well-known phonolitic laccolith of Traprain Law, East Lothian, beautiful crystals of apophyllite were discovered in drusy cavities. It was found possible to collect numerous specimens which are now in the Hunterian Museum, University of Glasgow (M 5970). There is no previous record from the locality and the following is a brief description of the rock and its associates.

Along with the apophyllite occur well-formed icositetrahedra of analcime. A thin section reveals that the apophyllite is of later crystallization than the analcime. The latter mineral lines the walls of the cavities, with which the apophyllite is seldom in contact. Radiating fibres of pectolite are occasionally seen on the surface of the analcime.

The metamorphism surrounding the granite of Carn Chuinneag in eastern Ross-shire provides the classical example of polymetamorphism in which a regional metamorphism is superimposed on a normal thermal metamorphism.

Prior to the regional alteration a pelitic facies of the Moine sediments suffered metamorphism of a purely thermal type in the vicinity of the granite. At a subsequent date the whole region was involved in fold movements with the production of crystalline schists. In this deformation the belt of rocks surrounding the granite yielded in such a way that belts of the hornfels zone moved en masse and are preserved amidst rocks which are now typical crystalline schists, and all stages of transition between genuine hornfelses and typical micaschists can be traced in the field.

Well-Crystallized icositetrahedral garnets from Botallack, Cornwall, are preserved in most British mineral collections, but they have previously not been systematically examined. The original specimens were discovered in 1821 by a St. Just miner who dealt in minerals, and the occurrence is first referred to by Carne in his paper 'On the mineral productions and the geology of the parish of St. Just' as follows : 'About six months ago, a mass of beautiful garnets, of a deep red colour, was found imbedded in the rock, not far from low water mark at the foot of Chycornish Carn, about a quarter of a mile south of Botallack. Some of the crystals were larger than hazel-nuts, and most of them were twenty-four sided. Some specimens of a very superior order were procured, each having from one to two hundred crystals on its face.'