f. Selenium, in an open glass tube, gives a red deposit of selenium.

g. Tellurium, in a similar glass tube, gives a greyish-white crust of its oxide.

h. Arsenic gives off a greyish-white vapour, which smells like garlic.

i. Quicksilver, in a glass tube, will be precipitated in minute metallic globules.

k. Water, from hydrous minerals, deposited by condensation in the same manner.

4th. The colour of the flame when the tip of the blue part is neatly directed upon the mineral; whence may be distinguished

a. Red tint, given by several minerals containing strontia and (?) lithium.

b. Green, produced by some phosphates and borates, sulphate of baryta, some copper ores and tellurium ores.

c. Blue, given by chloride of copper, chloride of lead, &c.

5th. The development of magnetic properties after treatment in the reducing-flame, as in ores of iron, nickel, and cobalt.

So far the assay has been considered by itself, but it is frequently necessary to mix it with fluxes, either to render it fasible or to produce a glassy compound of a characteristic colour.

Thus if borax or microcosmic salt be fused into a glass at the end of a platinum wire bent into an eye, and a little powder of the unknown mineral be added to it, we shall obtain by the use of the oxidizing flame the following results:

Manganese, in all its compounds, gives a beautiful violet or amethyst colour.

Cobalt causes a sapphire-blue colour; chromium an emeraldgreen.

Oxide of iron produces a yellowish-red glass, which becomes paler as it cools, and at length grows yellow or disappears.

Oxide of cerium gives a red or dark-yellow colour, which also grows paler as it cools.

Oxide of nickel renders the glass a brown or violet tint, which after cooling becomes reddish-brown.

Oxide of copper in very small quantity gives a green tint, which grows blue in cooling.

Oxide of uranium renders the glass bright yellow, which in cooling takes a greenish tint.

Oxide of antimony gives a pale yellow colour, which soon disappears.

When soda is used as a flux, it is generally upon charcoal, and by this aid the metals may be obtained from most of their combinations in a pure state. For this purpose the powdered ore is either mixed with the moistened soda in a paste, or is enveloped in a piece of thin paper which has been dipped in a solution of soda. After fusion, that portion of the charcoal which has absorbed any of the fluid substance is to be cut off and ground down with it in the mortar, when the metal, if malleable, will at once be recognised. If several metals are combined, of which one is more easily oxidized than another, as for instance lead when combined with silver or copper, the latter may be separated by adding metallic lead or boracic acid, according to circumstances, and maintaining a continued oxidizing flame, till the whole of the lead has passed into the state of litharge.*

We will now suppose the voyager landing upon some coast, and desirous, among other things, either of adding to our knowledge of minerals or their localities, or of discovering ores of the useful metals or coal. With respect to many minerals and the ores of the metals, it fortunately so happens that precisely the same places may be searched, and these are cracks and fissures, or those dislocations of rocks known as faults, either partially or wholly filled with mineral matter. Should he see before him such veins as a

* By means of more complete apparatus and extended operations, the most exact assays may be undertaken with the blowpipe; and those who desire a further insight into the subject may consult Plattner's Art of Assaying by the Blowpipe;' Berzelius On the Blowpipe;' and the above-mentioned work by Von Kobell of Münich,all of which are translated into English.

and b traversing the rocks of a cliff, he should not neglect to land there. If any hollow spaces present themselves, let him there search for the crystalline minerals. The vein a is represented as filling a fault, the dislocation having brought different rocks into contact; and we may suppose, for illustration, that c is porphyry, and d some schistose rock. The fissure b is intended to be a mere crack. Often when dissimilar rocks are brought into contact, mineral substances are found in the fissures, and this is a point which the voyager should not neglect. In certain countries the occurrence of the ores of the useful metals is not unfrequent under such conditions. On tidal coasts, should a vein of this kind be found productive, it may be desirable to wait for low water to trace the direction of the vein among any ledges or rocks which may be then laid bare. This may give the run of the vein inland, but not with certainty; for though fissures or faults may take general lines on the large scale, they, as would be expected, are very irregular for minor distances.

Should crystals be found in any such vein, it is often desirable to ascertain how they occur relatively to other bodies, crystalline or otherwise. Whole groups of crystals are thus frequently seen placed on certain projecting surfaces, facing one direction, and this as well on surfaces of crystals of other substances, as upon the sides of the vein, or walls, as they are technically termed. Such modes of occurrence are found as well in what, in common terms, may be called a horizontal as a vertical manner. They are not due to the drippings of water charged with the matter of the minerals in solution, such as are often seen in fissures, the re

sulting deposits being more or less crystalline according to conditions; on the contrary, the particular modes of occurrence to which we allude, seem more the result of crystalline deposits from solutions (filling the whole or a large part of the fissure), so acted upon, that projections in a given line, more especially if composed of certain substances, received these deposits in fact much in the same manner as substances in solution may be thrown down by well-known methods when galvanic action is employed. We have before us an illustrative specimen from the Consols Mine, Gwennap, Cornwall, in which large crystals of quartz are on the one side covered by crystals of sulphuret of iron, and on the other by crystals of copper pyrites. Cases where crystals of one substance abundantly occur on one side of prior-formed crystals of another substance, and not on the reverse or opposite sides, are sufficiently common, and best seen in the fissures or mineral veins themselves.

Although when exposed to the action of weather, the minerals which may be found in veins or fissures, open on the faces of cliffs, are not very often (except when of substances not easily injured) in a good state of preservation, they show that such minerals are found in the vein, so that if time and opportunity permit, some unexposed part of the vein may be broken into. Success may not, certainly, always attend such a search, for it is curious to observe how very local, even in the same vein, the occurrence of a particular mineral may be.

In collecting minerals in a vein, should a boat be at hand, so that they may be readily taken to the ship, it is better not to limit the specimen to some mere crystal itself, but to break off some of the body (either part of

the vein or of the rock, as the case may be) upon which it has been formed, so that when more leisure may be obtained, any illustration the whole specimen may afford of the manner in which the mineral may have been formed, should be preserved. By such specimens we often learn the history, as it were, of the mineral accumulations which, taken together, may, wholly or in part, have filled up a fissure. In this way it may often be seen that crystalline coatings of many substances have successively covered each other up towards the centre of the fissures.

The contents of veins are far often from being definitely crystalline; thus quartz and other mineral substances, such as the ores of many metals, have an amorphous appearance, their deposit having been effected under conditions which did not permit their particles to adjust themselves in definite crystalline forms. Again we find that, during the filling up of veins, fragments of rocks from the sides or upper parts of the fissure have dropped in; by their want of contact and by their isolation in many parts of the vein showing that this happened when the mineral or minerals thrown down from solutions were accumulating. A mineral vein sometimes forms a complete breccia, and this as well from the cause just assigned as from the mere filling up of the chinks left by fragments from the adjoining rocks, accumulated in the fissure before any deposit of mineral matter from solutions was effected. As might be expected, both varieties are to be sometimes seen in the same vein. Ores of the useful metals, such as sulphuret of lead, copper pyrites, and peroxide of tin, may, and do, as well form the cementing matter of such fragments, as common quartz, carbonate of lime,