The suite of dikes that forms the subject of this paper is bounded on the south from Sleights Moor (south of Whitby) to Dalston (south of Carlisle) by the well-known series of dikes known collectively as the Cleveland-Cockfield-Armathwaite dike, and on the north by the nearly parallel and more continuous Acklington dike which stretchesfrom Bondicarr near Coquet Island across the southern margin of the Cheviots into Scotland.

In a brief account of the Johnston-Lavis collection of Vesuvian minerals, now preserved in University College, London, Dr. K. W. Earle mentions ‘a large number of specimens of “Thermokalite”, a new member of the Haloid group, which has, apparently, so far escaped description.’ This previously unpublished name was copied from Dr. Johnston-Lavis's manuscript labels. The late Dr. H. J. Johnston-Lavis (1856-1914) possibly considered that this mineral was the potassium compound corresponding to thermonatrite [Na2CO3.H2O]. A provisional name for an undetermined mineral having, in this way, unfortunately been published, it seemed desirable to clear up the matter. For this purpose Dr. Earle very kindly supplied two good specimens of the mineral for investigation. Access was also given to the note-books kept by Dr. Johnston-Lavis. He had made a separate entry for each specimen and the carbon copies were placed with the specimens. The entry for ‘thermokalite’ reads in every case : ‘Thermokalite (n. sp.) by Tunnel nr. Stufe di Nerone, Baja.’ This locality is situated about nine miles west of Naples in the Phlegrean Fields (Campi Phlegraei).

Introduction—Opinion is divided as to the true crystal symmetry of diamond. Some authors, notably Fersman and Goldschmidt, who have investigated its morphological and etch characters, consider it is always hemihedral, whilst others, by the same methods, have obtained results which indicate holohedrism. Early work by A. Artom showed that it was seldom piezo-electric, but more frequently pyro-electric. Van der Veen also carried out avery thorough investigation and found no piezo- or pyro-electricity in his five diamonds. These were octahedral in shape, and not very suitable for this experiment.

Accurate knowledge of the compressibility of solids was first due in a large measure to the investigations of T. W. Richards, who showed that the pressure-volume curves for sodium and potassium approximate in form to rectangular hyperbolae, that the compressibilities of the free alkali metals are nearly proportional to the atomic volumes, and that the atoms can be treated as filling the available space. Richards then endeavoured to calculate the relative volumes of the combined elements in the alkali halides, assuming that the large contraction which takes place on forming the compound was due to an internal pressure which affected equally the alkali metal and the halogen.