The behaviour of the zeolites on dehydration, and their capacity for absorbing other gases and vapours in place of the water removed, have formed the subject of numerous investigations, qualitative and quantitative, of various degrees of accuracy. In only a few cases have attempts been made to fit an equation to the experimental data. Of these equations, those proposed by O. Weigel, G. F. Hüttig, and O. Schmidt are quite inadequate, as is readily seen by a trial with the more extensive data now available. On the other hand, E. Rabinowitsch derived an equation which proved capable Of reproducing the experimental data and is very similar to the equation now proposed, but derived in a quite different way.

Towards the close of the Carboniferous period in Britain, igneous activity, which had been prominent from time to time throughout the system, broke out afresh in a new form affecting a large area of the country between the Moray Firth and the River Tees. This activity was entirely, hypabyssal in character, the intrusions consisting of basic dikes and sills belonging without exception to the tholeiite magma-type of Dr. W. Q. Kennedy and W. Wahl. Those in the north of England include the famous Whin Sill and have been studied in great detail, particularly by Professor A. Holmes and by Dr. J. A. Smythe. The same cannot be said of their Scottish representatives. They possess, indeed, an abundant literature and several excellent publications deal with the intrusions of limited areas, but there is no connected account of them as a whole. Many districts, in fact, appear to have escaped investigation almost completely.

Ferrosilicon is occasionally found under circumstances that suggest that it is a natural mineral. Twice during the past quarter of a century it has been described as a new mineral, and the error was detected only after preliminary accounts had been published. It has also at times been thought to be meteoric. A supposed meteoric iron from North Carolina was described by C. U. Shepard in 1859 as composed of a material to which he gave the name 'ferrosilicine'.

The following notes collected during several years contain nothing new. They are merely brought together to serve as a warning against an error that may recur.

On several occasions between 1924 and 1929 Mr. H. N. G. Cobbe, a consulting mining engineer, sent to me for identification rounded pieces of a metallic substance that had been picked out from the concentrates of the gold dredgers on rivers and creeks in British Guiana.

At the suggestion of Professor H. H. Read the optic axial angle and the refractive index y were measured in four hypersthenes from Aberdeenshire norites. As the values obtained suggested that the minerals were iron-rich, it was decided to have chemical analyses made. These and the optical data are set out in table I below. At the same time the literature has been searched for analyses and optical data of enstatites and hypersthenes, in order to supplement those used by A. N. Winchell in his diagram of variation of the properties of the series. The references given by Winchell have been examined, and it is found that some of the data is not reliable.

Numerous veins and veinlets of epidosite traverse the crystalline schists and associated igneous rocks of the Malvern complex. They art fine-grained, compact rocks, of uniform texture and pale greenish-yellow colour, and vary in composition from almost pure epidote to mixtures of epidote with small quantities of quartz, sphene, sericitic mica, apatite, and, in almost insignificant amount, albite.

Analytical investigation of these rocks revealed the fact that the epidote they contain holds its water more tenaciously than has hitherto been suspected : the determination of water-content by the methods usually applied to the analysis of rocks and minerals gave results which were so seriously low as to suggest that the mineral was essentially anhydrous. Though more drastic methods increased the yield considerably, they failed to liberate more than about 75 % of the amount of water which, theoretically, should be present.