In submitting other crystals to the influence of compression and traction, I have found great numbers which do not exhibit the least 1race of transparent streaks and lines, the separate particles being merely dragged into lines, and exhibiting only a quaquaversus polarization. On the other hand, there is another class of crystals whose powders or particles are forced into distinct and transparent streaks and lines, in which the individual particles have a quaquaversus polarization and no trace of a prismatic arrangement. As these crystals have a peculiar relation to those in the preceding list, I shall enumerate the most important of them in the following table; that is, those in which the powder has been dragged into transparent and continnous streaks and lines, resembling externally portions of a solid body; for it is only by a comparison of the physical, or perhaps the chemical qualities of the two classes of bodies, that we can expect to explain the new property which is possessed only by one of them.

As both compression and traction are necessary in producing the transparent streaks and lines in both classes of the substances I have

enumerated, it became interesting to ascertain what effect was produced by each of these forces acting separately, and which of them was chiefly influential in developing the doubly refracting arrangement exhibited by the substances that possessed it.

The force of compression was undoubtedly the agent in forcing the separate particles into optical contact, while that of traction drew them into a line, and tended to dilate the film in the direction of that line, and to draw its particles from each other; or overcome their attraction of aggregation in that direction. It is quite possible, too, that these forces may have exercised some influence in modifying the doubly refracting structure of the substance under examination; but as such a question has no bearing upon our present subject, I have not attempted its solution.

Without expecting any very interesting result, I submitted to examination several of the soft solids which possess double refraction, such as bees' wax, oil of mace, tallow, and almond soap. The last of these

substances, though in common use, is a very remarkable one. Owing to its particles not being in optical contact, it has a fine pearly lustre, and may be drawn out into long and slender strings. Upon laying a portion of it on glass, it has a quaquaversus polarizing structure, with a tendency to form circular crystals; but when it is drawn out into strings, and laid upon glass, these strings have neutral and depolarizing axes, like the streaks formed by compression and traction. In the present case it is by traction alone that this crystalline arrangement of the particles is produced.

In oil of mace and tallow a similar effect is produced by compression and traction. With bees' wax the depolarizing lines are still better displayed, and the effect is considerably increased by mixing the bees' wax with a small quantity of rosin.

As the preceding experiments place it beyond a doubt that the optical or crystallographic axes of a number of minute particles are dragged by pressure and traction into the same direction, so as to act upon light like regular crystals, it became interesting to discover the cause of phenomena which certainly could not have been anticipated from any theoretical principle with which we are acquainted. The primary force, and indeed the only apparent one exerted in these experiments, is a mechanical force; but it is not improbable that a secondary force, namely, that of electricity, may be generated by the friction which accompanies the forces of pressure and traction. That such a force is excited with certain crystals will not admit of a doubt; but even if it were developed in every case, this would not prove that electricity was the agent in producing the phenomena under consideration. In subjecting asparagine to compression and traction, I observed, upon placing it in the polarizing microscope, that its particles were moving about under an electrical influence, but in no other case did the same phenomenon present itself to me.

The experiments with soft solids, but especially those made with the almond soap, exclude the supposition that the electricity of friction is the cause of the crystalline arrangement of its particles; though it is not improbable that the sliding of the particles upon one another, as produced by traction, and their mutual separation, as in the case of

tearing asunder mica or paper, may produce enough of electricity to have some share in giving the same direction to the axes of the particles.

When a portion of almond soap is placed upon glass, the axes of its particles lie in every direction, and have no tendency to assume the crystalline arrangement. The forces of aggregation emanating from three rectangular axes, are not strong enough to overcome the inertia, as we may call it, arising from the natural quaquaversus adhesiveness of the substance, and from the water interposed between its particles; but when the portion of soap is drawn out into a thread, these resistances to crystalline arrangement are diminished; elementary prisms, or crystals whose length is greater than their breadth, will have a tendency to place their greatest length in the line of traction; and all lateral obstruction to the play of its natural polarities being to a great extent removed, when the substance is drawn into a capillary thread the molecules will have free scope to assume their natural crystalline arrange.

ment.

The application of these views to the powders and particles of hard crystals is not so readily apprehended; but when we consider that the pressure brings the molecules of the substance within the sphere of their polarities, and that the force of traction reduces the compressed film into separate streaks and lines, like the threads of the almond soap, we have reason to conclude, that, even in hard substances, the atoms, when released from their lateral adhesions and brought into narrow lines, will assume the crystalline arrangement.

In the course of these experiments, I have observed in some cases where the crystalline arrangement was very imperfectly effected, a tendency in the atoms to quit their position, as if they were in a state of unnatural constraint, like the particles of silex and manganese in certain kinds of glass which experience a slow decomposition. If this should prove to be the case, either partially or generally, which time only can show, it will doubtless arise from the non-homologous sides of the elementary atoms having come into contact; a condition of the crystalline lines perfectly compatible with the existence of neutral and depolarizing axes, and of the colors of polarized light, provided that the non-homologous sides in contact deviate from their proper position, either 90° or 180°. If we cut a plate of mica, for example, into two pieces, and combine them by turning one of them round 90° or 180°, polarized light transmitted through them perpendicularly will exhibit the same colors as when they were in their natural position, and also the same neutral and depolarizing axes. If the polarized light is transmitted obliquely, the hemitropism of the combination, as we may call it, will be instantly discovered by the difference of color of the two plates.

II. GEOLOGY.

1. On the Gold Fields of Victoria or Port Philip; by H. G. WATHEN, Esq., Mining Engineer, (Quart. Jour. Geol. Soc., vol. ix, p. 74, communicated by P. N. JOHNSON, Esq., F.G.S.)-General Description, Geographical and Geological.-A chain of mountains, or rather a series of distinct ranges, runs round the southeastern corner of Aus

tralia, nearly parallel to the coast line, and from fifty to eighty miles from the sea, forming part of the main chain of the continent, and rising at its highest summit, Mount Kosciusko, to 6500 feet above the sea-level. This mountain chain in Victoria consists of clay-slates, mica-slates, and flinty slates, in successive steps, forming collectively, a recurring series.

The slates are nearly or quite vertical, with a north and south strike, and are intersected by numerous quartz-veins, running at an acute angle with the slates. Vast plains of trap, forming high table-lands, run up to the base of the mountains and probably cover their lower slopes. It is in the valleys and gullies of these mountains, and not very far from their junction with the trappean plains, that the rich deposits of gold are found. The auriferous districts are commonly broken by deep valleys and precipitous steeps. The hills are thickly forested; the soil poor and gravelly, and the surface strewn with anguJar fragments of white quartz.

Gold-fields.-Gold has been found at several points remote from each other along this zone of mountains; but incomparably the richest deposits hitherto opened in the Colony of Victoria, and indeed in the entire continent, are those of Ballarat and Mount Alexander, the latter far exceeding the former in extent and richness, while even the former is said by Californian miners to surpass in richness and yield all that they have witnessed in that region of gold.

Mount Alexander gold-field.-Mount Alexander lies in latitude 37° South, longitude 144° 20′ East, and is about 75 miles north-west of Melbourne. It was named by the first explorers Mount Byng, and is thus distinguished on many maps. It is a rocky granitic mountain, with a rugged flattened outline, towering some hundreds of feet above the summits of the forested ranges of slate-rocks which surround it, and of which it is the centre and nucleus.

The enormous amount of gold which this district has yielded has chiefly been derived from two valleys with their lateral gullies and ravines. These valleys are known by the names of the streams or "creeks" that run through them. One of these, Forest Creek, takes its rise in Mount Alexander itself; the other, Fryer's Creek, has its source in the high and broken ranges of slate that environ the Mount. Both Creeks are tributaries of the River Loddon. The workings extend five or six miles along the valley of Fryer's Creek, and about ten along that of Forest Creek. At Fryer's Creek gold has been found in large quantities beneath the bed of the stream, near its source, in the upland gullies. Forest Creek, on the contrary, appears to grow barren as it approaches the higher granite country, where it originates. On the banks of the River Loddon gold is found in small quantities, lodged in the crevices of the rocks, but no large deposits have been met with on the river, and even the stream into which Forest Creek runs, though itself only a feeder of the Loddon, proves far less rich than Forest Creek and its mountain affluents. In short, it would seem that the gold had been arrested in the small mountain ravines and gullies, and was never washed down to the large streams. Auriferous sands on riverbanks or in alluvial plains are unknown in the Colony. When within 12 inches of the surface, the gold is disseminated in a quartzose

gravel; when found at lower depths, it is almost always imbedded in clay, usually of a very tenacious kind.

Ballarat Gold-field.-The Ballarat gold-field, which is about fiftyfive miles north-west of Geelong and Port Philip Bay, lies at the junction of the slates with the trappean country, about seven miles from an extinct and now forest-grown volcano, known as Mount Boninyong. A second similar black volcanic mount rises out of the slate ranges, about ten miles due north of Boninyong. Granite crops out in small patches between the two Mounts.

This auriferous tract is united to that of Mount Alexander by a succession of similar dark forested ranges, rough, rocky, and sterile, strewn over with quartz, and consisting of the same series of micace. ous, flinty, and clay-slates.

Volcanic tract.-At the western base of these sombre hills lies a large tract of the most fertile and beautiful country-the garden of Australia Felix-the rich soil of which is the product of decomposed lava. These park-like plains, sprinkled over with groups of trees, are diversified by numerous domelike lava hills, without trees, but of the richest verdure. I have counted no less than twenty-four of these remarkable bold hills from the summit of one of them. The south and east sides are commonly steeper than the others. They are usually flat at the top; but in one of them, which I named Mount Lyell, after the illustrious geologist, there is a small crater, which had the reputation of being fathomless, but which I found to be in fact about 50 feet deep, consisting of an upper cup or crater about 15 feet in diameter, contracting below into a narrow rocky shaft or well, 30 feet deep, and three or four wide. The freshness of the traces of the flow of the lava, which is of a soft and perishable kind, indicates that the epoch of igneous action cannot be very remote. Altogether this volcanic region forms a most interesting subject for geological research and speculation.

Quartz Veins.-The sedimentary rocks are traversed by numerous veins of quartz, about 3 feet wide, of unknown length, in some districts descending to an unknown depth, in others not more than three or four feet deep. These veins or dykes run N. and S., or N. N. E. and S. S. W., and always make an acute angle with the lamina of the slates. They seem to be the original matrix of all the gold found in the valleys and creeks. The quartz is often intersected by many joints and narrow fissures, filled with a red ferruginous earth, in which particles of gold are disseminated. Gold is also found implanted in the quartz itself, and attached to the sides of its cavities. These auriferous veins were discovered and wrought before the alluvial gold deposits or "Diggings ;" and as they were worked with profit by the rude means at the command of the untrained diggers, they would doubtless well repay those who may operate upon them with all the appliances of modern European mining, so soon as the existing social excitement shall have subsided and wages shall have fallen from their present extravagant height. The first gold-working in the Colony was on a quartz vein running through one of the trappean plains so common in this country. The auriferous quartz is not milk-white, but has a delicate yellowish color, and a waxy lustre. That which is much broken and fissured appears richer than SECOND SERIES, Vol. XVII, No. 50.- March, 1854.

36