Mesolite was first recognized as a separate species by J. N. Fuchs (1816), being one of the three species into which he subdivided R. J. Haüy's species mesotype (1801). Its individuality has been repeatedly doubted, many workers regarding the mesotype group as an isomorphous series with natrolite and scolecite as the endmembers, and mesolite merely an intermediate isomorphous mixture. The frequent occurrence of intergrowths of mesolite with natrolite or scolecite is largely responsible for this confusion, these intergrowths frequently passing for single minerals, and being adduced as evidence of the occurrence of all intermediate compositions in the supposed isomorphous series. Faroelites, and mixtures containing faroelite, have also been analysed as mesolite from time to time.

During my mapping for the Geological Survey in 1930 of the metamorphic rocks of western Unst, numerous small masses were encountered that were composed of a central part of talc followed outwards in order by zones of actinolite, chlorite, and biotite. Whilst revisiting the island in 1933 I was able to examine these associations in detail and to collect abundant material for study. As in many cases the zones are made up of a single mineral and may be a foot or so in thickness, specimens of great beauty are obtainable.

In the following list of 41 lives, with a range in ages from 45 to 94 years, the average age is 70.7 years. Including previous lists, the average of 424 lives is 65.4 years. As shown in the following table there has been a gradual increase in this average during past years.

This new mineral was first found by a miner named Cann in 1903 or 1904 on the 480-foot level of the Bultfontein mine at Kimberley. It occurred, associated with calcite, apophyllite, and natrolite, in a large ‘horse’ of dolerite and shale fragments enclosed in kimberlite. This huge inclusion, several hundred feet in height, undoubtedly formed part of the country-rock that now encloses the kimberlite pipe. The Specimens of the new mineral were considered to be natrolite and were presented to Mr. A. F. Williams. Several years later the same mineral was found by Mr. C. E. Adams in the Dutoitspan mine, which is located about half a mile from the Bultfontein mine; he presented his specimens to the MacGregor Museum at Kimberley. Recently, Mr. Miller, Underground Manager of the Jagersfontein mine in Orange River Colony, discovered the new mineral in that mine, which is located 100 miles south-east of Kimberley.

The present communication deals with a peculiar series of rocks found in association with the Tertiary sediments so extensively developed in south-west Persia at the head of the Persian Gulf. At one or two localities in that region the marls and limestones are baked, fused, and in some cases so thoroughly recrystallized that at one time they were suspected to be igneous material arising from localized volcanic action. Careful examination of the field occurrences has, however, failed to disclose any trace of volcanicity, whilst petrographical and chemical examination has shown that even the most coarsely crystalline types bear no resemblance to any known igneous rock.

My attention was first directed to these rocks by Mr. H. T. Mayo in 1926 when I was permitted to examine the material collected by Mr. B. K. N. Wyllie, to whom belongs the credit of first discovering these apparently unique occurrences, and to visit the localities, where additional material was obtained. The cause of the alteration of the sedimentary rocks at these localities is no longer operative, and is not apparent; that it may most probably be ascribed to the combustion of gas or oil long since extinguished has been made clear by the subsequent investigation of other localities where similar rocks have been, and are being, exposed to such action and have undergone similar changes in structure and mineral composition.

Thomsonite was first recognized by H. J. Brooke (1820) in a JL study of the mesotypes or 'needlestones'. The 'needlestone' of Lochwinnoch and Old Kilpatrick, Dumbartonshire, was found to be an independent species, in addition to the natrolite, mesolite, and scolecite into which k. F. Gehlen and J. N. Fachs, and J. N. Fuchs, had divided the mesotype of R. J. Haüy. The new species was named thomsonite, in honour of Dr. T. Thomson, who analysed the material a few months later.

The published data on these three minerals, first found in the Laurion lead slags, is well summarized in Hintze (Handb. Min., 1915, vol. 1, pp. 2632-2641). In studying the original papers for the purpose of recalculating the elements of each, LaForge was impressed with their close crystallographic relationship in certain respects and with the curious complexity of the form series of fledlerite, which seemed to call for further observations. Accordingly, crystals of all three minerals from Laurion were studied on the goniometer, specimens loaned by the U.S. National Museum furnishing a welcome supplement to those found in the Harvard Mineralogical Museum. In the following pages the results of these studies will first be presented in brief form. Following this, the conclusion arrived at as to the most appropriate positions of the three minerals to bring out their mutual relationships will be stated.

The study of the materials from these two recently discovered occurrences has added much to the knowledge of meteorite craters. The two present many points in common and they supplement one another. At Henbury there is a much better development of the meteoric iron, while at Wabar the silica-glass predominates.

In the memoir dealing with the geology of the Broken Hill district, New South Wales, mention is made 1 of a remarkable rock type found in a few places in the vicinity of Broken Hill, which looks not unlike an aplite in the field. A brief description of its appearance in thin section is given. It consists mainly of what appears to be very basic plagioclase. A fair amount of quartz, some epidote and bluishgreen hornblende were noticed, whilst a notable amount of sphene is present.

The accurate analysis of an igneous silicate rock is a task beset with difficulties and one which, on account of the very complete analyses now required by petrologists, involves the expenditure of a considerable amount of time. The advantages which accrue from the performance of quantitative analytical operations on the micro-scale are becoming more and more apparent, and the application of at least semi-micro-analytical methods to rocks was thought to have profitable possibilities, particularly in the way of hastening the analyses.

The present investigation began with an attempt to isolate and analyse the small sparse anorthoclase insets (t)henocrysts) of the chilled glassy selvage of a felsite dike. On comparison of the compositions of the insets and the host rock it was found that the relationship was abnormal and that the insets could not have grown in a magma represented by the glass. The composition of the felsite interior of the dike, however, represents a magma which could have yielded the anorthoclase, and full consideration leads to the conclusion that the glass, though absolutely fresh and unaltered in appearance, has suffered marked changes in composition.

In 1924 S. G. Gordon described as a variety of thomsonite a pink zeolitic mineral occurring as a fine crystalline powder in cavities of augite-syenite at Narsarsuk, Greenland. The material was described as orthorhombie, with two good cleavages a(100) and b(010) and a less perfect one c(001) ; no other faces were observed on the minute prismatic crystals. The refractive indices Gordon measured as ± 1.535, ² 1.537, ³ 1.545, with the optic orientation a = b, ² = ±, ³ = c, and optic sign positive. Analysis gave the figures under I (p. 307), and as these agree with the composition to be expected for a potassiferous thomsonite, apart from the high water content, Gordon regarded it as such, and gave it the varietal name kalithomsonite.

During the last year, Dr. R. H. Rastall has been engaged on an investigation of the mineral content of certain sandstones of Middle Jurassic age in north-east Yorkshire. These sandstones proved to be unusually rich in the titanium minerals rutile and anatase. In some samples the proportion of the last-named is greater than in any other specimen previously recorded, so far as can be ascertained. Some of the heavy-mineral separations also contained a number of crystals of quite unmistakable brookite, with normal crystallographic development and normal optical properties, namely Bx perpendicular to (100) and intense dispersion ρ > v. Associated with these, however, there were often observed a number of smaller crystals of very similar appearance, whose optical orientation seemed to be entirely different. In particular, no optic picture could be obtained, and the extinction between crossed nicols in parallel light was perfectly sharp, with no suggestion of strong dispersion. Dr. Rastall therefore asked me to carry out some further investigations into the nature of these crystals, which were unlike anything he had previously seen in sedimentary rocks.

The spherulitic rhyolites of Jersey show a development probably unequalled in the British Isles. They are particularly notable for the large size of the spherulites and for the variety of structures which they present. The object of the present paper is to describe some of these structures and to discuss their origin.

The first worker to publish a description of spherulitic rhyolites from Jersey was Davies (2). Their field relations were described by Noury (4), while De Lapparent has discussed their petrology (5), (8) and the vexed question of their age (7). Parkinson (10), (12), (14) has given admirable and detailed accounts of the Bouley Bay rocks.

The very rare barium zeolite edingtonite was described by W. Haidinger (1825), and named in honour of Mr. Ed.ington. Haidinger's material consisted of small crystals on thomsonite from Dumbartonshire. An analysis by E. Turner indicated a calcium aluminosilicate, but there was a loss of 11·22 %. The crystals (sp. gr. 2·71) were morphologically tetragonal, with the prism m(ll0) and sphenoids p(111) and n, and an axial ratio c/a = 0·6725. A. Breithaupt (1832) gave the name 'Antiëdrit' on account of this Symmetry,

It has recently been shown by W. Nieuwenkamp that matlockite is identical in chemical composition and crystal-structure with artificial lead fluochloride PbFC1. His conclusion is based upon powder photographs of the two substances and a fluorine determination of a specimen of matlockite from Matlock, Derbyshire. The present work was undertaken primarily to check Nieuwenkamp's interesting results. Access to an exceptionally fine suite of matlockite specimens in the British Museum collection made possible single crystal X-ray measurements, accurate optical determinations, and a new chemical analysis.