It is more than twenty-one years since Mr. Allan B. Dick communicated a description of the microscope, now generally associated with his name, to this Society. The instrument is familiar to all mineralogists, and it will suffice to say that the main feature consisted in having the polarizing and analysing prisms arranged so that they can be rotated simultaneously, instead of turning the object on the stage between them. The rotating stage is never very satisfactory, especially when it is desired to examine minute crystals in convergent light. In two pamphlets, published later, Mr. Dick extended his description of the instrument and gave some methods of using it.

Among the chief treasures of the University Museum is a large piece of the meteoric stone which fell at or near Chandakapur in the valley of Berar, India, on June 6, 1838. The specimen has been for many years in the collection, but there seems to be no record of its acquisition or previous history. The weight was formerly 3329.5 grams, but the stone was cut in two in 1899 and a portion exchanged with the late Mr. J. R. Gregory for a number of representative specimens of meteorites. A series of five thin sections were prepared at the same time, and about five grams of fragments remained, which have been used for the analysis described below.

In the present notes the writer has endeavoured to collect all the available facts concerning the occurrence of zeolites in both Cornwall and Devon. Specimens belonging to this group are rarely represented in collections of Cornish minerals, and as several new localities have recently come to light, the following observations will, he ventures to hope, be of some interest as adding to the already lengthy list of mineral species occurring in the West of England.

The crystallographic and other physical characters of seligmannite from the well-known quarry in the Lengenbach, Binnenthal, were first described by Professor Baumhauer in 1901. In its crystallographic characters the mineral was found to be closely allied to bournonite, which it resembled in the habit of the crystals and the repeated twinning on the prism-planes.

When investigating the morphology of crystals, such as those of schwartzembergite, which are so rounded or striated as to afford no definite reflections of the object-slit of the goniometer, the author found most serviceable a camera lucida which could be attached to the eye-piece of the telescope of the goniometer, and thus used for the direct drawing upon paper of the ‘light-figures’ given by the crystals, the ordinary signal being replaced by a pin-hole. The cap of the eye-piece in use is unscrewed and the camera lucida is fixed to the tube by means of four clamping screws.

In a single homogeneous crystal the physical character of parallel lines are everywhere the same, and it may be justifiably assumed that the orientation of the crystal-structure is constant throughout. Compound crystals, however, occur in which the orientation of the crystal-structure is different in different parts although they consist of the same substance.

This difference of orientation may either be original or result from the action of mechanical forces on the crystal-structure. I shall in the first place assume that the former is the case.

It is usual to divide axes of rotatory symmetry into those of the first and those of the second sort. In the former a crystal is brought into coincidence by a rotation through a certain angle round the axis and in the latter by such a rotation followed by a reflection about (or, as I prefer to say, a reversal relatively to) the plane at right angles to the axis. In 1906 Mr. H. Hilton proposed to define an axis of rotatory symmetry of the second sort as one in which the rotation was followed by an inversion about (reversal relatively to) a point, and he showed that his proposal would, if adopted, simplify the definition of the crystallographic classes.

The change suggested relates mainly to the representation of the faces below the plane of projection. I propose that every face below that plane shall be represented by the same point as a parallel face above it.

If the two parallel faces are equivalent they will both be indicated by the same circular dot (accompanied, if desired, by the indices of either face). If they are not equivalent and only one be present, it will be represented by a plus sign (+) if it be above the plane of projection, and by a minus sign with a dot in the centre (-) if below it. If both are present but not equivalent, the double sign (±) will be used.

At the Emily coal pit, Arniston, Midlothian, a heap of shaly refuse from the workings became spontaneously ignited some time ago, the cause being presumably the evolution of heat by atmospheric oxidation of iron-pyrites. As a result of the slow combustion of the shale, accompanied as it is by liberation of sulphuric vapours, a number of uncommon mineral-species have been formed and deposited as sublimates in the cooler parts of the heap. The credit of discovering these minerals and recognizing their unusual character belongs to Mr. A. Craig Christie, F.L.S., from whom the specimens in the Royal Scottish Museum were obtained.

In the course of his official work in the Lizard district, Dr. J. S. Flett collected various samples of minerals which were handed over to me for examination. Two of these specimens proved to be datolite remarkably well crystallized. As this species, now rare in Britain, had not been recorded before from Cornwall, although pseudomorphs of chalcedony after it—the well-known haytorite—are mentioned by Greg and Lettsom from North Roskear mine, Camborne, the facts of its occurrence seemed well worthy of further investigation. Accordingly, in October of last year, Dr. Flett and myself paid a visit to the locality, where we succeeded in obtaining a large amount of the material.