All petrologists who have worked much with the microscope must have felt the want of a system of micro-chemical analysis ar once simple and reliable. Having devoted some time to the study of micro-chemical reactions, I think it may save the time and labour of students who propose to take up the subject if I give them the result of the experience I have gained up to date.

In a former communication to this Society, I have demonstrated that quartz must now be added to the long list of minerals in which a lamellar structure can be set up by mechanical stresses. In that paper, a crystal of smoky quartz was described in which well marked lamellæ could be detected; the relations of these lamellæ to the parts of the crystal which had suffered mechanical deformation and crushing are such as to leave no possibility of doubt that the lamellar structure is not an original but a secondary one; while it is equally clear that the structure has been developed by the action of mechanical forces upon the crystal.

Probably everyone who has considered the arrangement of the constituents of an aggregate composed of radially grouped fibres has realised that the individual fibres are conical or pyramidal in form, their apices meeting in the centre of the aggregate. In a coarse example of this mode of erystallisation, such as the calcite concretions in the magnesian limestone of Durham, this conical form of the constituent crystals is very easily seen; the cones cleave across, where composed of a cleavable mineral, showing that the particles composing them have the same orientation within the limits of the cone, and that each cone, in fact, is a crystal, bounded ultimately by contact with its neighbours.

My friend, Mr. A. T. Karslake, sent me recently a pareel of crystals from Ceylon, amongst which was a brown tourmaline showing the very rare face z =, (first recorded by Haüy), on whose existence so much doubt has been thrown. The crystal is about ½ inch across, and about ¼ inch in the direction of the axis, and shows well the hemimorphic development. At the analogous pole are r{100} and z, both largely developed, also o {111}, e {110}, s, .

Some time ago I was informed that galena was being obtained in a sandstone quarry at Aimville, about two-and-a-half miles north of Kirknewton, which had been recently re-opened for the purpose of supplying building material in connection with the extension of the Harperrig Reservoir, belonging to the Edinburgh Water Trust. As I saw no likelihood of my soon being able personally to visit the spot, I mentioned the fact to my friend, Mr. Alex. Lumsden, M.E., who I knew had sometimes occasion to pass near the locality, at the same time telling him that I did not attach much importance to the alleged occurrence, and that I did not expect that it would be of such interest as to be worthy of a special visit. Subsequent investigation showed, however, that I was mistaken, and as the mode of occurrence of the mineral is so unusual, some account of it may not be without interest.

The mineral which forms the subject of this communication came from the gem mines of Rakwana, Ceylon, and was brought to England by Mr. Joseph Baddeley, who, while superintending operations there, had formed a collection representative, it was believed, of almost every kind of pebble to be found at the works. This collection Mr. Baddeley, on his return home, submitted to Mr. Pringle at the Museum of Practical Geology, London. In looking, from time to time, over the collection, Mr. Pringle had occasion to take the specific gravity of some of the specimens. Amongst those so tested were certain pebbles the sp. g. of which was found to be about 3.98. This resuIt, combined with their other physical characters, having rendered it impossible for Mr. Pringle to assign them to spinel, ilmenite, or other species with which he could compare them, he handed the pebbles over to me for chemical analysis.

Shortly after the Meeting of June 16th, at which Mr. Dick gave the description of the characters of Geikielite, Mr. Joseph Baddeley, who had brought the specimens from Rakwana (or Rackwanné) (80°40' E., 6°25' N., in the District of Kollonnagam, Ceylon), courteously offered to present one of them to the British Museum for preservation in the Mineral Collection: the rest of his small store of eight or nine stones, picked out by him from a heap of other dense pebbles, he required for sending as samples to those friends in Ceylon whom he wished to interest in a search for further material.