Professor Heddle remarked, that this title would sound strangely, to southern ears; as in England and probably also in Ireland, the putting money enough in the pocket, and proceeding to the shop of a dealer, was the ordinary, and indeed the all sufficient method; though some enthusiastic collectors might go so far as to visit the openings of mines; while some adventurous ones might even explore them. In Scotland no such method of procedure could be adopted; there were absolutely no mineral dealers now in Scotland; there were almost no mines, and of these none now yielded minerals of special interest.

In carefully reviewing the various facts which I have been able to collect since the publication of my paper on the microscopical Structure of Crystals, I have been led to believe that many peculiarities in the structure of granitic rocks may be explained by a principle, which, as far as I am aware, has not hitherto attracted attention. It appears to me extremely probable that the critical point in the consolidation of granitic rocks is very closely connected with the critical temperature at which highly heated and compressed steam would condense into an equal volume of highly heated and expanded liquid water.

As I pointed out in the paper already mentioned, rocks melted under great pressure probably contain water either dissolved as a gas in a liquid, or in the state of a fused hydrate. On cooling down to a lower temperature, the crystallizing out of anhydrous minerals would almost necessarily set free this previously combined water. As long as the temperature was above the critical point it would necessarily remain more or less disseminated in the rock as highly compressed steam, but as soon as the temperature fell below the critical point, it would condense into highly expanded liquid water.

I have been lately examining in conjunction with Prof. Hull a a large series of lavas from Vesuvius, which were collected by Prof. Ouiscardi, of the University of Naples, with a view of determining whether, in the space of 300 years, any difference had occurred in the composition of the lava flow. In the course of this investigation a much more important question arose, viz. :—What is the proportion of each mineral present in the lava, and why does that proportion exist ?

The rock is composed of unknown quantities of nine minerals, of known composition viz.: Leucite, Plagioclase, Magnetite, Olivine, Augite, Hornblende, Mica, Nephcline, and Sodalite, together with an unknown quantity of a paste of unknown composition; from which it is easy to shew that the unknown quantities exceed the number of equations; and consequently, the discussion of the composition of the rock belongs to a branch of the Indeterminate Analysis.

A Ms. Catalogue of Minerals by the Comte de Bournon has lately come into my possession. From internal evidence the date of the volume may be fixed at 1811—three years after the publication of the Count's Traité de Minéralogié. The collection of minerals described in this catalogue was made for the Government of Brazil ; if the collection still exists, a careful comparison of some of the specimens in it with their descriptions in the catalogue would clear up some obscure points and lead to useful results. Without this aid to a clear understanding of Bournon's descriptions, many interesting facts may be gathered from the manuscript in question. It is, however, a voluminous work extending over 356 pages, and illustrated with a large number of careful drawings of crystalline forms. The author was a very laborious compiler of catalogues. One of these, known to the present writer, is still in existence in the Town Hall of Devonport, along with the magnificent collection of minerals (the St. Aubya collection) to which it refers. A few notes on the Brazilian catalogue may not be without interest.

To the geologist, the mineralogist and the chemist, two of the observations made during the voyage of the Challenger are of especial interest. One of these observations is the occurrence over vast areas of the deep sea bottom of a peculiar red clay, containing silica, peroxide of iron, and alumina. The other discovery to which I refer has been described by Sir Wyville Thomson as the occurrence throughout this red clay of nodules of “nearly pure peroxide of manganese.” To these nodules, as well us to the red clay, an organic origin has been assigned. But the immediate source of so much manganese is hard to find, for this element is by no means an abundant constituent of animal or vegetable organisms. The difficulty is, however, somewhat lessened when the manganese nodules are submitted to a more minute chemical examination. From two correspondents I have received an ample supply of these curious concretions, accompanied by a suggestion that they should be submitted to chemical analysis.

This mineral was first observed by Mr. C. E. Wilkinson, the Government Geologist, and obtained by him from a cutting on the Bathurst Road, near the Cox River.

It occurs as small irregular veins, of a pleasing salmon eolour, running through a soft bluish grey shale, the veins together with the included plates of shale are sometimes six inches thick, but usually smaller; the actual veins of the mineral itself being only about one eighth of an inch thick. Some difficulty was on this account experienced in obtaining sufficient of the sample pure enough for analysis.

The mineral appears to be partially crystallized, nothing definite could be made out, but some of the confused crystals had somewhat the appearance of rhombic prisms. It apparently cleaves parallel to the long axis, and lies perfectly at right angles to it.

As black tourmaline or “schorl” is one of the most abundant and widely distributed of the minerals of the West of England, it is perhaps somewhat remarkable that the variously colored and colorless varieties are extremely rare both in Cornwa]l and Devon. Among recorded localities, I am not aware that the green or brownish green Zeuxite has occurred, except at Huel Unity, Carn Marth, and Great Work Mine, in Cornwall, and near Okehampton in Devon, while the colorless variety Achroite has only been observed at Roscommon Cliffs, in St. Just; and the red, blue, and yellow varieties are so far quite unknown in the two western counties. I have lately been examining a number of specimens obtained in a large open tin working at Rock Hill, in the parish of St. Austell, Cornwall, in 1871 and 1872, and among them I have found several specimens of Achroite. When I first obtained them I thought they were quartz, and, indeed, I referred to them as such in a paper which I read to the Miners’ Association of Cornwall and Devon, in 1872, but I am now satisfied that they are colorless tourmaline or kchroite.