For many years past Mr. R. H. Solly has been accustomed to spend each succeeding summer in the quest of mineral specimens in the neighbourhood of the village of Binn, Switzerland, particularly of those occurring in the white crystalline dolomite of the Lengenbach quarry, and his patient energy has been rewarded by the discovery, not only of material which has thrown fresh light on previously known minerals, but also of specimens which on examination proved to represent species new to science. Especially important was the discovery in 1903 of small, and often minute, blood-red crystals which differed both in colour and in streak from realgar, a common mineral in the quarry.

During the last twelve years I have communicated to this Society, often in collaboration with Dr. G. T. Prior, several papers descriptive of Bolivian minerals. These papers have dealt primarily with the species augelite, andorite, argyrodite, stannite, and chaleostibite, though many others have been examined and in some cases incidentally mentioned. The latter, as being of lesser general interest, or as not having led to sufficiently important results for separate publication, are now collected together in the present notes.

One of the peculiarities of Bolivian tin-ores is the frequent occurrence of cindery and cellular masses of cassiterite, which is presumably of secondary origin. But, apart from impressions of quartz crystals, definite crystal-forms are rarely shown by this pseudomorphous cassiterite.

The pseudomorphs to be now described are from the Tres Cruces district, and were collected by my son, Mr. A. W. Pearce. The crystallographic determinations have been made by Mr. L. J. Spencer, and the specimens examined by him have been presented to the British Museum. The material consists of cavernous masses of dark brown, finely crystalline and granular cassiterite, associated with which is a pale yellow, ochreous substance.

To the north-west of Rathdrum, in the county of Wicklow, three important groups of lead mines were formerly worked, which are known respectively as the Glendasan or Luganure, Glendalough, and Glenmalure mines, after the mountain glens in which they are situated. The lodes traverse the granite in a north and south direction close to its junction with the mica-schist, and are somewhat remarkable for the variety of their mineral contents.

The Silvermines mineral district is situated along the northern base of the Silvermine Mountains, five and a half miles south of the town of Nenagh in the county of Tipperary. The district is one which possesses somewhat remarkable features, of interest to both geologists and mineralogists. The mines extend over a narrow tract of country for a distance of about five miles along an extensive E. and W. line of fault, in which Silurian, Old Red Sandstone, and Carboniferous rocks are brought into juxtaposition. This line of fault has been traced for a distance of about thirty miles from Gallows Hill in co. Clare, on the west, to Toomavara in co. Tipperary, on the east. Along its course in at least two places mineralization has taken place, resulting in a somewhat complex series of contact-lodes and metasomatic deposits.

The instrument described in this paper is identical in principle with the small refractometer designed by the author more than three years ago, but differs from it in several details which are of considerable practical importance. As in the earlier form, a compensative lens is introduced of such curvature and focal length that the focal surface of the optical combination is a plane within the range for which the instrument is required, and consequently the critical edges are sharply defined in monochromatic light for all positions. It will be more convenient, before entering into the description, to take the features which have been changed.

If a straight line making an angle with a zone-axis of a crystal be rotated about the zone-axis while the crystal remain fixed, the physical characters of that line will pass through a cycle of changes. If these changes repeat themselves n times during the course of a complete revolution, the zone-axis is said to have an nth-turn or n-fold cyclic symmetry. If the line be at any time normal to a crystal-face it will be normal to a face with the same physical characters n times during such a revolution.

The rock-specimens here treated were collected in 1902 on a small plateau near the head of the Oberer-Bach, where the rock is in place. This stream, rising near the Röckner or Reckner, a summit of the Tarnthaler-Köpfe on the north of the Tuxerthaler mass, flows down a steep ravine southward to join the Schmirner-Bach: the locality is situated about 20 kilometres to the south-east of Innsbruck. The figures 2629 (height in metres) on the ‘Generalstabskarte’ probably represent the site of the plateau ; it is on the right bank of the stream, close to, and some 12 or 15 metres above, a small frozen lake near the head of the stream. The point was reached by ascending the ridge from the Kreuzjöchl. There was much snow on the plateau and the geological relations of this particular occurrence were not observed.

Some years ago the writer received from St. Joseph du Lac in the County of Two Mountains, province of Quebec, Canada, a few small specimens of a black mineral which was identified as magnetite. Later, a more careful inspection of the fragments, which weighed from tell to fifteen grams each, showed that some of them were portions of crystals made up of an unusual combination, the octahedron {111} and a trapezohedron {311}. Further, chemical analysis showed that the composition was specially interesting, the mineral being titaniferous and containing, besides 3.24 per cent. of magnesia, a larger proportion of manganese than had been observed in the case of anymagnetite previously examined.

During recent years a systematic survey of the mineral resources of Ceylon has been in progress, in connexion with which a large number of specimens have been sent to the Imperial Institute for examination. In 1905 several cases containing coarse gravel from the streams of the gem-district of Balangoda were received. The constituent minerals were mainly zircon, tourmaline, corundum, spinel, ilmenite, together with small quantities of geikielite, fergusonite, and other rare-earth minerals. Last summer during the examination of these gravels one of the authors found three black crystals witll unusually brilliant faces. The apparently monoclinie form and the general physical characters at once suggested the crystallized native zirconia, baddeleyite, and this conjecture was confirmed by the goniometrical measurements and the chemical analysis.

The deposit known as the Wheal Sedgman lode is inclined to the west a few degrees from the vertical, and runs in a direction about 10° W. of N. (magnetic) through the parish of Perran Uthnoe, near Marazion, Cornwall. In its course seawards from the approximately E. and W. lode formerly worked in the Great Wheal Neptune mine, it traverses the North and South Trebarvah tin and copper lodes. It is crossed by the shore-line on Perran Sands, about 500 yards to the west of Trevean cliff. Between that spot and Cuddan Point, to the S.E., where it is again laid bare, it has been superficially removed by marine denudation. The numerous N. and S. diabase dikes of the district show in placts much disseminated pyrrhotite, and one of them runs nearly parallel to the east side, or foot wall, of the Sedgman lode.

In a paper read before this Society in 1904, dealing with a number of new minerals from the Binnenthal dolomite, Mr. R. H. Solly described under the name of bowmanite some small, honey-yellow crystals belonging to the rhombohedral system and forming either hexagonal plates or combinations of rhombohedron and basal planes of octahedral habit. Mr. Solly afterwards handed over the small amount of available material to me for further examination.