The author exhibited and described the small additions that need be made to an ordinary microscope, in order to make it available for the above-named purpose, and also gave a few illustrations of its application to particular minerals. So far, however, the instrument has been used only sufficiently to prove that the method gives excellent results. The author thinks it desirable to defer a complete decription of the construction and use of the instrument until he has been able to examine a sufficient number of minerals to publish a table of their indices of refraction for practical use. It may, however, be well to say that the addition to the microscope consists only in a small graduated scale attached to the body of the instrument, and vernier to read off to th of an inch. This enables us to measure the extent to which the focal length of the object glass is increased by looking through a more or less transparent miueral, and also its thickness in the part thus examined.

Quite recently I obtained from an importation of Japauesa curiosities two pairs of chop-sticks which were catalogued and sold as jade. Under this name arc often included, not only the true jade or nephrite, with a hardness of 6 and a specific gravity approaching 8, but also three other mineral species. Of these jadente is not only harder but heavier than jade : prehnite differs but slightly from jade in either of these characters; while flour, the remaining species referred to, has a hardness of 4 only. Had the specimens to which I now direct attention belonged to any of the foregoing species, they would have been worthy of notice on account of their extraordinary size, or rather length, and also by reason of the beauty of their appearance. But after I had determined these objects to be serpentine, I thought some particulars as to their characteristics might prove of service in identifying one of the materials employed in oriental art.

All minerals are supposed to be either magnetic or diamagnetic, and in a large number, exact measurements have been made of the relative amount of magnetic three in each mineral. As was to be expected, the compounds of Iron and Nickel are, in the great majority of cases, the cause of the magnetism in mineral ; but there exists a large border land of slightly magnetic mineral substances, the cause of whose magnetism has never been very clearly shown. I do not intend, in this paper, to deal with those which are only faintly magnetic, but with those whose magnetism is quite distinct, such as Obsidian, Basalt, &c. The method used for testing the relative amount of magnetism in any specimen was as follows.

In a paper lately communicated to the Chemical Society, I endeavoured to show that an exact examination of the rate at which water was expelled from hydrated substances at any constant temperature, might teach us much as to the constitution of these bodies. One of the bodies examined was the mineral Gypsum, which has been found in three different states—first, in its most usual form as Ca SO4, 2 H2O, or as it should be written 2 Ca SO4, 4 H2O as iu selenite ; second as 2 Ca SO4, H2O in which three of the molecules of water have disappeared, as in certain un-namcd forms of Anhydrite ; and third as Ca SO4 as in Anhydrite. Now these three can also be obtained by artificial means ; the second being found in steam boilers where the water is evaporated under pressure; so I made several attempts to obtain the other two possible hydrates, 2 Ca SO4 3 H2O, and 2 Ca SO4, 2 H2O by evaporating solutions Under different pressures, but I could obtain no satisfactory results.

About two years ago, while working at the crystalline form of a number of chemical substances of which I could obtain only small quantities, and in consequence minute crystals, I found that a great deal of time and trouble were lost in consequence of having the use of only one goniometer. When a crystal was fixed in its place by canada balsam and carefully centred,—a tedious operation when carried on under the microscope, as I had generally to do,— its angles measured and description noted, I found I often wanted to keep it for comparison, but before another could be examined, the first had to be taken off and half an hour spent before the second could be got into a satisfactory position, the first being very often spoilt in being removed, or even if still entire, much time must be lost before it can again be referred to. Now the possession of half a dozen instruments would obviate all this, but few chemists can afford the luxury of such a number of goniometers, and unfortunately so few possess one at all that it is seldom that such a thing can be borrowed.

Whilst detaching a small crystal of leadhillite for examination with the polariseope, from a specimen brought from the Leadhills, Lanarkshire, which came into my possession some years ago, I observed one side of the mass to be more or less encrusted with a thin drusy coating, which, from its hardness and streak, I was led to suspect might be either the above species, or Laxmannite, described in 1868 by Nordenskiöld in the Journ. f. prakt, chem. of that year.

The bulk of the specimen consists of massive greenish pyromorphito mingled with cerussite, upon this occurs the vauquelinite. The remaining minerals are lanarkite, leadhillite, caledonite in tufts of minute acicular crystals, massive black eerussite and quartz.

In the autumn of 1871 I found in a large cavity or “vugh” in the schorlaceous granite of Boscaswell Downs, in the parish of St. Just, Cornwall, a number of black and opaque hexagonal prisms, having ragged terminations, which I at first took to be pseudomorpbs of black tourmaline (schorl), after quartz. They were set aside for further examination and forgotten until the beginning of the present year, when I undertook their examination.

I found that, although they were very compact, the sp. gr. was only 2.747, which at once negatived the idea of schorl, the sp. gr. of which ranges from 3.0 to 3.3. I then cut a number of sections for microscopic examination, and these at once shewed that the prisms were composed of clear and eolourless quartz, containing an immense number of tourmaline crystals, mostly very thin and arranged in feathery groups as in Plate III, figs. 1 to 4.

Since my communication on this subject published in the first number of the Mineralogical Magazine, I have made further observations, and have found other specimens greatly varying, but all embodying the same general principle of solid quartz enclosing the oxides of iron.

The quartz is perfectly solid, breaking with its usual eonchoidal fracture, and though richly colored with the oxides of iron disseminated through it in beautiful forms, is itself transparent, so that the forms and colors of the iron are well seen. The colors are various shades of red, yellow, amber, grey, &c., and [hose colors are distributed in well-defined forms, and not in mere tints as in the case of amethyst, &c.

The Volcanic Rocks of Lower Silurian age in the Lake District are interesting in the highest degree on many accounts, and not least so on that of the extreme metamorphism which they have undergone, partly by the deep burial they suffered during the period between the close of the Lower Silurian and the Old Red, when they were once more largely uncovered, and partly by that neverceasing action of infiltration, decomposition, solution and replacement to which all rocks are subject during the course of geological time, but to which rocks of an originally volcanic origin seem specially subject.

If there is one feature in this metamorphism of the Cumberland rocks more prorainent than another, it is the large degree to which chlorite has been developed among them, and the universality of its occurrence.

This quartz, the precise locality of which is unknown, is different to any that I remember having previously seen. It is apparently from a mineral vein, and consists of an assemblage of quartz pyramids, which differ from the usual form in having each angle apparently supplemented by a small prism, giving to the centre block a curious stellate appearance, fig. 8, Pl. V.

The interspaces arc filled up with minute pyramidal crystals of quartz, as well as others of chalybite and pyrites.

The fractured under surface fig. 7 shows an infinity of concentric lines of growth, the interior being composed of transparent quartz, while the outer layers are milky and opaque.

It is a well-known fact that Pyrrhotite, or Magnetic Iron Pryrites, frequently, if not invariably, contains nickel, generally with cobalt in various proportions, amounting together from traces, up to nearly six per cent., and that most of the nickel of commerce is derived from this mineral

The following notes contain in the first place the results of the examination of a few varieties of pyrrhotite, occurring in Nova Scotia, New Brunswick, and the United States, chiefly with reference to presence or amount of nickel and cobalt, and they shew also that remarkable differences exist in the intensity of the magnetism displayed, which ranges from distinct polarity in the mass, down to very iceble attraction by a magnet in the finely powdered state of the mineral, and further, that the most feebly magnetic of the specimens examined is that containing the largest per centage of nickel. The subsequent notes relate to other species from h~ova Scotia and Newfoundland.