The petrology of the igneous rocks has for the last quarter of a century been established,on a sound quantitative basis, largely as a result of the body of experimental work available on silicate melts. In the field of metamorphism, however, progress has been much less marked, and the difficulties of the laboratory development of stresses comparable with those acting during regional metamorphism must for some time leave our knowledge of the crystalline schists far behind that even of the hornfelses. A quantitative approach, however, is not confined to the experimental side. The introduction of the conceptions of facies and grade raises a new need for exact knowledge of the compositions of the various minerals, both of those constituting the different isophysical assemblages of a given grade, and of the isochemical assemblages representing a given rock under the grade-conditions of the various facies established.

In the Mineralogical Magazine for September, 1930, Dr. Frederick Walker describes 'A tholeiitic phase of the quartz-dolerite magma of central Scotland'. Several pages of the article are devoted to a consideration of the phenomena he has observed in these rocks in their bearing upon certain views which I have expressed. In most respects Dr. Walker has clearly grasped the essential features of my thesis, and his efforts to obtain further information on the various points have been well directed. I am glad to welcome such a discussion as he has given, even though his conclusions are somewhat opposed to mine. In one respect, however, he has apparently overlooked an essential feature of my argument. On this matter, and on some points of evidence given, I should like to present some discussion. I desire also to examine certain other recent papers by Daly and Barth and by Bowen, Schairer, and Willems, in which the views expressed in my article have met with some criticism.

The meteorite is situated on the western slope of Marengi Hill, about 150 yards from the top of the hill and close to the boundary of Mr. Jennes's farm. This place is 10 miles south-east of the Mbosi mission station in Rungwe (formerly Langenburg) district. The latitude and longitude are approximately 9°7′ S., 33°4′ E. The locality lies between Lakes Tanganyika and Nyasa, south of Lake Rukwa, and about 23 miles from the border of Northern Rhodesia.

The contact-zone of Chalk and Tertiary dolerite at Scawt Hill, near Larne, Co. Antrim, consists of an assemblage of comparatively rare minerals, including a mineral of the composition Ca2SiO4 not previously recognized as a naturally occurring compound. In the assemblages of the contact-zone the chief minerals, apart from calcite, are spurrite, calcium orthosilieate (larnite), melilite (gehlenite), merwinite, spinel, perovskite, and wollastonite. Outside this contact-zone, the chalk consists almost wholly of calcium carbonate ; nearer the contact it is recrystallized to a granular mosaic of calcite of coarse texture, while at the immediate contact the chalk is completely transformed into an aggregate of new-formed silicates in varying proportions. A hybrid zone between the dolerite and the exogenous contact-rock is composed Of a coarsely crystalline rock built up essentially of titanaugite, melilite (humboldtilite), nepheline, wollastonite, perovskite, and various zeolites. An account of the melilite of this hybrid zone has already been given.

Ceylon moonstone is probably the best known variety of those alkali-felspars which display a prominent internal colour reflection or ‘schiller’. On account of its blue sheen and its clear transparency, the mineral has attained a certain degree of popularity and some value as a gem-stone.

The Indian peninsula, though considered to be a very stable part the earth's crust and hence called the 'Indian Shield', shows in different parts evidence of formerly having sustained epicontinental basins, in which sedimentation occurred. These sediments are now found in detached prisms as crystalline gneisses and schists in different parts of India, e.g. in the Madras Presidency, Bihar and Orissa, Central Provinces, Central India, and Rajputana. They have been found overlying the ancient gneigses (Archaean), and belong to a division known in Indian geology as the Dharwar System.

The specimen to be described was found in 1925 by Miss H. K. Cargill and Miss J. A. Ledeboer on a scree slope beneath a gully in the basaltic capping of the Slaufrudal granite-granophyre stock at Kvosafoss, SE. Iceland. Unfortunately the rock was not discovered in situ, but it must belong to the upper part of the stock or a dike apophysis of it. An examination of the rock was begun by Miss Ledeboer, but she was unable to continue the work; I am indebted to her for the photographs of pl. VII, figs. 1 and 2.

While I was engaged on the geological survey of the Postmasburg manganese fields during 1927 the rare mineral zunyite, a basic orthosilicate of aluminium, was discovered in some altered highly aluminous shales or flagstones. The only occurrence of zunyite so far known is in Colorado, where, according to Dana's ‘System of Mineralogy’, it was found at the Zuñi mine, Anvil Mountain, San Juan Co., and near Red Mountain, Ouray Co.

When the slip catalogue of the barytes specimens in the British Museum collection was in the course of preparation, a few observations were made which may be of sufficient importance to place on record.

The lists of localities of the barium minerals, barytes, witherite, alstonite, and barytocalcite, in the collection show that rather more than half of the specimens (573 out of 975) come from the British Isles. Hence it would seem that there is a special concentration of these minerals in this part of the world. Possibly this is fictitious, as the collection cannot be considered to be completely representative.

The phonolites which are found in the volcanic region of Dunedin, New Zealand, are of a varied character. Some of them are of ordinary types, but others are nephelinitoid, and some of them have sodalite in abundance. Besides the phonolites, there are trachydolerites, some of which also contain sodalite as well as nepheline. There is also an abundance of tinguaites, in all of which nepheline is distinct and sometimes sodalite as well. All petrologists who have worked in this region are therefore perfectly familiar with the minerals sodalite and nepheline in many different associations and conditions.

The Dhoon granite is contained in sheets 8 SW. and 8 SE. of the 6-inch Ordnance Survey Maps of the Isle of Man. It is a bosslike intrusion of irregular outcrop (fig. 1), enclosing an area about one and one-third miles long in an east-west direction, and half a mile wide in a north-south direction. It has been intruded into rocks which form part of that division of the Manx slates known as the Lonan Flags, and has metamorphosed these to a certain extent.

In the following pages an account is given of the rock assemblages produced at the contact of a dolcrite intrusion with chalk. Owing to the intense localized assimilation of calcium carbonate by the dolerite magma, unusual rock types are produced. The products of the endogenous contact-zone are dealt with in detail. Those of the exogenous contact-zone have in part been described already, but some additional data are incorporated in this account.

Although frequent references have been made during recent years to the ‘bauxite’ deposit of Jammu in Kashmir, no complete account giving its geological relations is yet available. The only published,account is that of Middlemiss, and Fox has also made brief references to it in his recent book on bauxite. Previous work on bauxite by the present writer induced him to examine these rocks, and through the kind intervention of Prof. W. W. Watts a complete set of them was obtained from the authorities in Kashmir. Only the petrological and chemical aspects of these specimens have been dealt with here, and consideration of any possibility of their economic use has been avoided.

A Magnificent specimen of melanterite has recently been presented to the British Museum by the generosity of Mr. James L. Bruce, Resident Director of the Cyprus Mines Corporation, through the agency of Prof. C. Gilbert Cullis of the Royal School of Mines, London. The specimen (B.M. 1930,439) appears to merit a short description, for it cons,ists of a group (35 by 25 cm.) of enormous greenish-blue crystals (up to 18 by 13 cm.) of a very unusual habit, being tabular to b(010). The photograph (fig. 1) can convey only a very inadequate idea of the beauty of the group, and it is most fortunate that the generous action of Mr. Bruce and the care of Prof. Cullis have ensured its preservation and exhibition for the pleasure of many.

The Dalton volcanoes include all the volcanic groups which rise up at the north-western end of Taiwan (Formosa). They are old extinct volcanoes underlain by highly disturbed Tertiary sediments. Among them Shichisei-zan is the highest and the most prominent, rising up to 1108.7 metres above sea-level. It is mostly made up of hornb]ende-andesite, hypersthene-hornblende-andesite, and agglomerates. On the western slope of this partly dissected volcano there is a very characteristic cone called Shabō-zan. Its elevation is 643 metres above sea-level, and it is mostly made up of hypersthenehornblende- andesite poured out through the thick accumulation of agglomerates. The andesite here has usually a grey colour, but often passes into a light reddish-brown variety, being sometimes associated with a noritic segregation mass. It is noteworthy that some of the andesites abundantly contain brown hornblende. This mineral also frequently appears, together with brown biotite, in the segregation mass.

It has long been possible to identify readily many minerals by means of density and refractive index determinations, and the chemical composition also can often be approximately deduced. Tilley has shown that it is practicable to determine any natural glass by this method and be succeeded in separating the natural glasses into groups characterized by certain limits of specific refractivity. As far as the author is aware, no such systematic method has been described for distinguishing the artificial glasses one from the other, and it is these glasses that we are concerned with in attempting to determine the approximate composition of an imitation gem-stone without the aid of chemical analysis.