In that part of the Gangpur State immediately to the north of the Bengal-Nagpur Railway, between Biara and Garpos, lies a tract of dolomite- and limestone-bearing country which has been referred, on lithological grounds, to the Cuddapah (? Algoukian or Palaeozoic) formation. From this area, all the dolomite and most of the limestone requirements of the Bengal iron and steel industry are at present derived, and the close proximity of the enormous haematite ore reserves of Singhbhum indicates a still greater economic importance for these materials in the future.

The stone was seen to fall, at about 1 p.m. on March 9, 1923, by a thatcher named Frederick Pratt who was working at the time in a corner os a wheat-field on Ashdon Hall farm, Ashdon, near Saffron Walden, Essex. He heard a strange ‘sissing’ sound, and, supposing an aeroplane was overhead, looked up and a second or two after saw what he thought was a projectile fall about thirty yards from him into the wheat-field a few feet from the farm-road, causing the earth to ‘fly up like water’. Three days later, in company with another worker on Ashdon tIall farm named Curven, he dug up the stone from a depth of about two feet.

The new crystalline compound triphenyl-bismuthine dichloride, described crystallographically by Mr. G. Greenwood (Min. Mag., 1923, vol. 20, p. 123), possesses the remarkable property of exhibiting crossed axial-plane dispersion of the rhombic ‘brookite’ type and circular polarization. For purposes of comparison, the author prepared specimens of the mixed Seiguette salts, which also exhibit crossed axial-plane dispersion together with circular polarization. The Seignette salts, sodium-potassium tartrate and sodium-ammonium tartrato, crystallize each with four molecules of water ill the bisphenoidal class of the rhombic system. They are truly isomorphous and form a continuous series of mixtures. The acute bisectrix for sodium-ammonium tartrate is normal to (001)and for sodium-potassium tartrate normal to (100). For all proportions of mixture containing 5 % and over of sodium-ammonium tartrate, the acute bisectrix is normal to (001).

Topaz, so common an accessory in tin lodes in all parts of the world, has hitherto been looked upon as comparatively rare in Cornwall. When massive, or even in the form of small, well-developed crystals, it is a mineral easily overlooked, or apt cursorily to be mistakcn for quartz.

The presence of topaz as a microscopic accessory in granite, greisen, and rarely elvans, from most of the Cornish masses, has been determined by Dr. J. S. Flett in the course of the work of the Geological Survey; while the late Mr. J. H. Collins was responsible for the record of other interesting localities.

In the present notes I have collected all the available information respecting its mode of occurrence and localities ; and have added several new ones, at some of which the mineral occurs in considerable mass, thus affording evidence that topaz is in Cornwall, as in the case of other countries, a comparatively common associate of cassiterite and wolframite, both in granite and sedimentary rocks.

In a discussion of the composition of glauconite, it was shown that the analyses of this substance can be represented in terms of simple molecular proportions, provided that the mineral is regarded as a mixture of a silicate containing the group R2O3 with a similar compound in which one equivalent of R2O8 is replaced with one equivalent of RO; the general formula being R2O. 4(R2O3, RO). 10SiO2. nH2O.

Work on the sedimentary iron ores collected during the preparation of the ‘Special Reports on Mineral Resources’, recently issued by the Geological Survey, made it necessary to review the composition of some of the chlorites ; but no evidence of similar replacement was found among the better-known minerals of that group.

A Minute, black fragment of material, taken by Dr. J. R. Sutton from a cavity exposed on a cleavage-surface of a colourless diamond from Bultfontein mine, Kimberley, South Africa, was sent by him for determination. It is black with a sub-metallic lustre and in parts a bronzed tarnish; and is quite opaque even on the edges. The form is roughly that of a triangular chip, measuring 11/2 by 11/4 mm. with a greatest thickness of about 1/2 mm. The weight is about 1 milligram. Tile surface shows a small and uneven to granular fracture. On one portion there is a good crystal-face which reflects a sharp image ; and on one part of this face there is a stepped growth with striae at 60°.

Although mining operations have been carried on in the Mendip Hills for a period of about 2000 years—probably since pre-Roman times, very little is known respecting the minerals that occur in the district. The reason for this is that most of the mines were exhausted previous to the development of mineralogy as an exact science; and furthermore only few specimens have been preserved in collections. During the nineteenth century operations were mainly confined to re-working the vast accumulations of refuse left by the earlier miners. This work was continued at the St. Cuthbert's Lead Works (1 mile ESE. of Priddy) up to the year 1908, since when all work has ceased on the Hill. The latest mining was for iron and manganese ores at Higher Pitts farm (1 mile SSE. of Priddy); here work ceased in 1893.

In Part I of this paper the actual frequency-distribution of igneous rocks as revealed by the latest edition of Washington's collection of analyses was examined, and compared with that of earlier records. An attempt wilt now be made to determine the law of this distribution–a necessary preliminary to any petrogenic application of the results. The silica frequency will be considered since this has been found to give a curve more characteristic of igneous rocks than does any other oxide Now Dr. Harker pointed out that the silica distribution of records published in 1903 did not obey any simple law such as that of the probability curve, and the same conclusion applies to the collection of 1917. However, when the empirical method of Karl Pearson was applied to analyse the curve into component curves of error, fairly simple conclusions resulted.

Mercuric sulphide, HgS, occurs in nature as two well-known modifications, cinnabar and metacinnabarite. The latter is some what rare and occurs as black cubic crystals possessing the symmetry of the zinc-bleude, i.e. the ditesseral polar-class. It is considered to be identical with chemically precipitated black mercuric sulphide, the density of both being 7.81. Cinnabar is of more common occurrence and is found as well-defined crystals and in the massive state. The crystals are assigned to the trigonal holoaxial class. The rhombohedral angle is 92°30' r correspouding to an axial ratio c/a of 1.1453. The crystals possess a very good cleavage parallel to the prism (21̄1̄)=(101̄0). The rotation of the plane of polarization, for red light traversing the crystal in a direction parallel to the optic axis, is 315° per millimetre, a value roughly eighteen times that of a similar thickness of quartz.

Through the kindness of Mr. F. W. FitzSimons, Director of the Port Elizabeth Museum, South Africa, pieces of this iron were placed at the disposal of the writer for examination and analysis. The original mass, weighing about 203 lb. (92 kg.), was found at Karee Kloof, about nine miles from Hofmeyer, Cape Province, South Africa, and was presented to the Port Elizabeth Musem by Mr. N. H. Ogilvie in 1914. From a cast which was made under the direction of Miss M. Wilman, Director of the McGregor Memorial Musemn, Kimberley, the dimensions of the mass are approximately 43 × 30 × 20 cm. It is very irregularly shaped, is pitted with ‘thumb-marks’, and is cavernous with depressions, one of which on the side shown in Pl. III, fig. 1, has dimensions of about 20 × 15 × 7½ cm.

A Remarkable pegmatite occurring on Bittleford Down (Wind Tor), near Widecombe, is described in the Survey Memoir as a veinrock containing (a) abundant hornblende, a mineral not previously found in any of the post-Carboniferous granites of the west of England, (b) much sphene, (c) porphyritic crystals of oligoclase, and (d) quartz crowded with fluid inclusions.

This rock is of peculiar interest in other respects. Its complete freedom from biotite and its high content of felspar (oligoclase dominant over orthoclase) imply considerable deviation in bulk composition from the normal Dartmoor granite. Moreover, its accessory minerals include both gold and silver.

Considered broadly as a coarse-grained felsic type, its position in the list of variants from the normal granite is shared by a still more felsic rock with which it is closely associated in the field.

Although there is an extensive literature on the amphiboles, especially those of the monoclinie series, there appear to be only few records for basaltic hornblendes in which the physical properties and the chemical composition have been determined in detail on the same sample of material, Mention may be made of the later papers by S. L. Penfield and F. C. Stanley, S. Kreutz, W. E. Ford, and H. Küchler.

The basaltic hornblende described in the present paper is found in the volcanic tuff-breceias of Pliocene age in the neighbourhood of Lake Balaton. The locality is near the small village of Balatonesicso on the southern slope of the ‘Fenyves’ hill, the top of which is capped with basalt. Tile hornblende is found as loose crystals in the tuff-breccia and also in blocks rich in olivine. Specimens of some size, up to 2 or 3 cm. in length, may be collected.

Mr. Alpheus F. Williams, General Manager of the De Beers Consolidated Mines, discovered in December, 1928, in the Dutoitspan mine, at Kimberley, crystals of a colourless mineral so different in appearance from other minerals observed in the Kimberley mines that it appeared to him to be new and worth detailed study. The mineral was found between the 500 and 750 ft. levels in a large dolerite inclusion in the kimberlite, and is associated with apophyllite, calcite, and natrolite. Up to the present time, less than a pound of the mineral has been found, and by far the larger part of this amount is represented by a few crystals of large size (11 × 4 × 1½ cm.). On closer examination, these crystals are seen to be not a single crystal, but a group of sub-parallel individuals, a type of development that is often observed on the larger crystals of many minerals.

This paper continues the study of the constituent minerals of the Dartmoor granite. The district to which it mainly refers comprises the for-area around Widecombe and a part of the aureole adjoining. No detailed reference will be made at this stage to aureole phenomena. The results to be recorded necessitate a brief description of the two main granite types and of their field relationships. Abundant varieties and modifications of both types occur, but for the Purposes of the present paper they are of subordinate importance.

Most of the for-masses and high-level exposures of granite in the area consist in the main of the type known locally as the ‘giant granite‘ — a very coarse-grained, strongly porphyritic roelc rich in biotite, and consistently garnetiferous; it has an index-figure 1 ranging from 7.5 to 12.

The optical dispersion phenomena of felspars at the alkalic and calic ends of the plagioclase series have been investigated by C. Viola and S. Kôzu, but for those of intermediate composition the data have been lacking. In view of the usefulness of the dispersion data of felspars for their determination in cleavage-flakes by the method to be described in the next paper, the present writer has made a study of the dispersion of certain intermediate plagioelases.

On the basis of field relationships, the main types of the Dartmoor granite can be referred to four stages of intrusion, the sequence being from relatively basic to thoroughly acid.

To this sequence is closely related an increase in the content of tourmaline and in the extent to which autopneumatolysis (with tourmalinization) was effective before solidification of the rock was complete.

Autopneumatolysis is well displayed by many minor intrusions referred to the latest stage. Such an intrusive rock is reddened more or less uniformly throughout its entire mass, and volatile constituents exhaled from its margin have reddened a contact-zone of the grey granite into which it is intrusive.