Among the minerals found in meteorites, there is none which has attracted the general notice to such a degree as the metallic nickel-iron, especially from the fact that it has hitherto never been seen for certain in any telluric rocks. Nay, so much stress was laid upon this latter circumstance, that such iron was thought never to occur here on earth without having been carried to us from the outer universe, and ever since Chladni's report on the iron-mass of Pallas, every loose block of iron lying on the surface of the ground, nay, even deeply imbedded in it, has generally been declared to be a meteorite, if it only contained a certain percentage of nickel and, which was not always the case, manifested some crystalline texture, called after the discoverer "Widmannstäitten's figures."

When in 1870 Nordenskjöld had made the discovery at Blaafjeld (Ovifak) on the Isle of Disco of the remarkable large iron blocks, there soon, as will be remembered, arose a whole literature on the occurrence and origin of this iron. Although the Danish naturalists had, from the first raised a series of objections against the theory of the meteoric origin of these iron-blocks, the problem of their existence could not be satisfactorily solved without careful geological investigations having been first made into the nature of the whole of the Greenland basalt-formation. Such investigations having been made by Mr. K. J. V. Steenstrup, I was directed by the Danish Commission for the Geological and Geographical Survey of Greenland to make a chemical examination of the materials collected.

Some mouths since I received from J. G. Grenfell, Esq., of Clifton College, a few small specimens of igneous rock which he had collected in the year 1880 on Old Providence Island. This is an island in the Caribbean Sea about 90 miles off the Mosquito Coast, in lat. 13°26'N, long. 81°18 W. Itis oval in shape, 4½ miles long from N to S, and 2¼ miles wide. Barely separated from it on the North is a little island named Sta. Catalina. Bit. Grenfell describes the main island as mountainous, with three chief peaks, the highest of which rises to 1,190 ft. Spurs from these terminate on the shore in peaked hills from 800 to 700 feet high.

Garnet is most commonly found in the form of separate crystals embedded in metamorphic rocks; occasionally, but comparatively rarely, in beds or veins. On a recent visit to the Pyrenees, in the Province of Catalonia, I found this mineral forming what appears to be a true dyke. I first noticed an outcrop of it in the steep banks of a brook, in one of the higher valleys of the main mountain chain. At this point it had the appearance of a vein, almost vertical and running nearly East and West ; the wall rock was a highly metamorphic schist, so that its stratigraphical relation to the garnet could not well be made out; however, the general strike of the strata in this district is about East and West.

This unusual substitution appears to have taken place in a rock found by Mr. R. N. Worth, F.G.S., on Trowlesworthy Tor. The specimen was a loose block, and the rock to which Mr. Worth has given the name of Trowlesworthite has not yet been discovered in situ. The rock consists of red felspar, fluor-spar, and tourmaline, associated with quartz, and its general character and microscopic structure are described in papers published in the Transactions of the Royal Geological Society of Cornwall, Vol. X. p. 177.

The deleterious effects of small quantities of Arsenic when present in Copper are weI! known to all who are concerned with the working of thin latter metal, and the elimination thereof is consequently an object to which the copper smelter pays special care. Though a large number of minerals, some of which are of exceeding beauty, are found composed of Copper combined with Arsenic acid, the direct combinations, as Araenide and Sulph-Arsenide, are comparatively rare.

It appeared of interest to determine the nature of the alteration which has changed the light greenish or brownish yellow siderite to the dark, almost perfectly black, glossy crystals so often seen on specimens from this neighbourhood.

The material, gathered from the heap of a mine, consisted of massive siderite, crystallised on its natural surfaces in the form of small curved primary rhombohedrons, and associated with quartz, pyrites, blende, and other minerals.

The rocks whose microscopic structure it described in this paper were collected by my friend, M. G. Stuart, Esq., during a tour in Australia, under the kind auspices of A. W. Howitt, Esq., F.G.S.,the well-known geologist, who has so largely added to our knowledge of one of the most interesting districts of that continent. Some of them have been already noticed by that gentleman, but as the volumes in which his descriptions are published are not very accessible to English readers, and as two of them are rocks to which I have devoted special attention, I have ventured to bring them to the notice of our Society.