In recent years there has been little essential change in the design of the petrological microscope. F. E. Wright directed attention to the improvement that could be obtained by using a full-sized condenser with a large polarizer, but the high cost of the latter seems to have restricted its use to a few special models.

With the introduction of ‘polaroid’, a thin, intensely pleochroic film mounted between glass disks, this restriction no longer holds. A polarizer can be supplied of sufficient size to cover an ordinary Abbe condenser, while the analyser no longer requires the compensating lenses which usually accompany a calcite prism, with the indirect result that the definition of the interference-figure is improved.

Lxullianite is well known, at least by name, in this country, and indeed it enjoys an international reputation among petrologists. Its general characters have been described by Bonney and Sir John Flett, while reference to the type is to be found in most standard text-books on petrology. It is, however, a rock of outstanding interest and deserves fuller description and illustration than have yet been accorded it.

The preparation by Mr. A. V. Weatherhead of a large set of thin sections for teaching purposes has given the writer an opportunity of making a more detailed examination of the micropetrology of the rock, with special reference to the manner of the replacement of the several original components.

The most complete succession of Carboniferous rocks found in Co. Limerick crops out in the Limerick basin, which is situated between Limerick and Tipperary. The zonal ranges of the chief lithological divisions of the Lower Carboniferous rocks have been determined, and two volcanic episodes, represented by the Lower and the Upper Volcanic Groups, are now known to have occurred early in S1 and early in D1 times. The porphyritic pyroxenes have been isolated from representatives of the lower group, which ‘constitute a graded series of olivine-basalts, trachybasalts, trachyandesites and trachytes, comparable with the Lower Carboniferous Scottish suite. Among the olivine-basalts, all the Scottish types have been recognised, with the exception of Craiglockhart type and mugearite.

In the course of an investigation on refractory materials, in which the identification of minerals by their X-ray diffraction patterns had a prominent place, an interesting observation was made on a zircon of gem quality which was lent to us by the courtesy of Mr. B. W. Anderson.

It may be recalled that the existence of three allotropes has been postulated in order to explain the considerable variations of physical properties which are found when comparing different specimens of zircon. In particular, densities ranging from 3·95 to 4·86 have been observed, the density of zirconium silicate, calculated from X-ray measurements, being 4·71.

Many of the experiments described in this paper were made in the course of an examination of problems arising in connexion with technical uses of fibrous asbestos, undertaken about three years ago at the request of Dr. W. Francis, at that time Director of Research for Messrs. Turner Brothers Asbestos Company Limited, Rochdale. We have recently been able to investigate in a little more detail certain points which seemed likely to be of fairly general interest, and we now present our results in the hope that they may be of use to other researchers in this field. We are indebted to Dr. Francis and his colleagues for valuable discussions on questions arising in the course of the work, and to the Directors of Messrs. Turner Brothers for financial assistance in connexion with the earlier experiments, and for permission to publish this paper.