A very ready method of distinguishing quartz crystals from a large number of others, is by trying if they can be scratched with a knife. Steel will not scratch quartz; and further, quartz crystals generally show a horizontal striation or striping on some faces of the hexagonal prism (at right angles to the longer axis of the crystal); they will moreover strike fire with steel.

As to the varieties of quartz, one has a peculiarly dark green colour, and is called "prase." Milk quartz is a translucent variety, owing its milky colour to a metal, and we can generally in it detect a slight reddish tinge. It differs from chalcedony in not having a blueish tinge. Where the shade of red is very distinct, the specimen generally has more transparency, and is then known as rose-quartz.

A very elegant variety, of a yellow colour, is the well-known Cairngorm. It much resembles topaz, but wants both the hardness and specific gravity of that beautiful gem. The specific gravity, for instance, of quartz being 2.6 to 2.7, while that of topaz equals 34 to 36. The hardness of quartz being 7 in the scale, and of topaz 8.

The mineralogist does not limit the term "amethyst" to quartz of any particular colour, but uses it broadly as indicating coloured varieties of semi-transparent quartz. Popularly the word designates a kind which is tinged of a delicate violet from the presence of manganese.

Brown quartz is valuable for the cabinet; many pieces, however, which appear to be of this colour, have only a deposit of oxide of iron upon the surface, removable by dilute hydrochloric acid. Quartz of a smoky tinge is often mistaken for beryl, but the latter has generally a peculiar horny yellowness as seen in the play of reflected light about the sides of the stone when held in certain directions. The beryl will, moreover, scratch quartz.

There is a beautiful stone which incloses minute fibres of asbestos, producing, when polished, a resemblance of flickering light, as seen in the cat's eye; this is only a fibrous variety of quartz, but is much prized. The difference between "cat's eye" and moonstone is simply this-the cat's eye has fibres in quartz, but the moonstone has them in felspar, which is a composition of quartz, alumina, and potash.

We often find the hollow flints lined with a pale bluish translucent substance, having what mineralogists call a "botryoidal" surface, like that of an aggregation of soap bubbles (or the surface of a bunch of grapes); this is chalcedony, and very handsome pieces are met with in shingle. Sometimes, in cavities, the chalcedony has in form much the appearance of icicles or a "stalactite." Layers of coloured chalcedony occur in

nature, and where such are straight or only slightly curved, the stone is called "onyx;" and in this figures are carved out of one layer, leaving another of a different colour as a background. Such carvings are the well-known "cameos." Stones in which an opaque white alternates with a deep or orange brown which is tolerably translucent, are called the "sarde onyx;" and in the estimation of the lapidary, the more translucency, the greater the value. "Sarde," itself, is a very beautiful and frequently met with variety of quartz, of an orange or amber yellow, or more commonly of a reddish yellow, and is only semi-translucent. Some specimens when moved in certain directions, possess in a considerable degree that beautiful play of light already referred to as chatoyance, and much resemble opals of the same colour, but are both heavier and harder. The richest shore for variety in this species of stone is the back of the Isle of Wight, from Niton to Bonchurch, although larger and elegant specimens of some sorts are obtainable between Walmer Castle and Sandown Castle, at Deal. What is knowi as "plasma" was formerly used in making ornaments; it is dark green, having lighter coloured spots. (Its specific gravity is only slightly above 2.0.) Bloodstone, or heliotrope, is a fine well-known variety of chalcedony, tinged green with chlorate, and has irregular dots and markings of bright blood-red jasper. A very pretty apple-green quartz is called chrysoprase; its colour is not uniform, but clouded, and the stone has considerable translucency.

The difference between chalcedony, carnelian, jasper, and agate, is often scarcely appreciable. The name carnelian was originally given to specimens of a flesh colour, but it is now extended to the brown and yellow varieties. Numbers are brought from the East Indies, but very beautiful specimens are found on the beach at Deal, and especially near Deal Castle, and opposite the dockyard. Carnelian is never figured nor striped; the deep, clear red is the most valuable for the purposes of the lapidary.

When layers of chalcedony, instead of being straight or nearly so (as in onyx) are suddenly interrupted by angles or sharp curves, the stone itself having some considerable translucency, such are termed agates, and many are of great beauty. They are never perfectly transparent. A general characteristic of agate in its rough state, is the resinous or waxy appearance of its fracture, while that of quartz resembles more the glitter of broken glass.

Scotch pebble is agate of an agreeable reddish tint, free from cloud or mark, and is semi-transparent. When without small flaws, to which it is very liable, it polishes into a handsome stone of good surface. When agate contains mossy or

branched internal markings, it is known as moss agate or mocha stone.

In some parts of England whole masses of agate rock are composed of layers of chalcedony or milk quartz in small but intricate convolutions; when these layers are of some dimensions and present angular flexures, they so much resemble the bastions of a fort, that the name "fortification" agate has been aptly applied to them. At St. Just, in Cornwall, this rock may be seen in situ.

The mixture of iron with flint or quartz gives it a considerable change in appearance, causing an opacity characterizing the bulk of fragments which form a shingle beach; and such is jasper. The prevailing colours are red and yellow, but it is also found of a deep rich brown, or even nearly black, and sometimes green. The bright pure yellow and the light scarlet are the most prized, although the latter seldom occurs except in small portions, but it is very elegant. Coloured layers are known as ribbon jasper; and when these layers are concentric, the stone is called Egyptian jasper, the yellow generally occupying the central portion of the stone. (All the varieties of quartz receive and retain a brilliant polish.)

A singular combination of quartz and water forms the "opal." A trace of water is detected in quartz, but in opal it amounts to as much as 10 per cent. Hence the lighter specific gravity of this mineral as compared with quartz, while its hardness is about that of window glass. The varieties of opal are sufficiently hard to be found among shingle. One is the "cacholong," of a milky white, and nearly transparent, distinguishable from milk quartz by its opacity and by its slightly adhering to the tongue. The "noble" opal is a very elegant gem, having colours combined in flashes of delicate lake, blue, and yellow. When the red greatly predominates it is termed "fire" opal. Common opal is abundant as fossil wood, and on some coasts may be procured in pieces of considerable size; it is easily detected by its showing the grain of wood, and being too hard to be scratched by a knife.

The only specimen of "felspar," besides the moonstone already mentioned as a constituent of granite, and worthy of present mention, as liable to occur in shingle, is the "Labradorite," a greyish or dull greenish stone, very slightly translucent, but when broken, and especially when polished, showing a pleasing iridescence. Like quartz, it takes a high polish.

The "smoke" beryl is found on almost all the south coasts of England, even so far round as Garrison Point, Sheerness. It slightly exceeds the quartz in hardness, otherwise it might easily be mistaken for opal.

This short summary of objects in shingle would be incom

plete without mention of another subject, which requires the use of the pocket lens. For example, if we examine some localities we shall find rounded flints having perforations in various directions, not through the stone, but into it; on breaking some of these, the interest and curiosity are deeply attracted by the frequently found, perfectly well preserved and petrified remains of exquisite corals, sponges, etc. Indeed, the needle-like spicula of sponge are often in these nodules seen of the greatest conceivable delicacy.

Indescribably beautiful specimens of what the late Dr. Mantell called the "choanite," are obtainable in some beaches. If you find an oval, flattish stone with generally a rough exterior, having its roughness (on close examination) caused by minute, short curved lines, suspect the presence of the choanite; lay the stone in the hand (protected by a glove, handkerchief, or any soft body) and strike the specimen at the middle of the thinner and longer edge of the oval, with a small hammer. One or two smart taps will split the stone through its longest section and thus reveal the interior, the wetting of which will render it more plainly visible. There is no limit to the colour, and variety, and form of these beautiful fossil polypes. I believe Sandown Bay, in the Isle of Wight, to be the richest deposit in England of this remarkable class of objects; they are there met with in that beach of the size of three, four, or five inches in diameter.

DR. WALLICH'S AMOEBA VILLOSA.

BY HENRY J. SLACK, F.G.S.,

Member of the Microscopical Society of London.

My object is to lay before the readers of the INTELLECTUAL OBSERVER Some account of Dr. Wallich's Amaba villosa, a remarkable Rhizopod on which three papers have appeared in the Annals of Natural History, and which I have had some opportunities of examining myself. I hope that by thus directing the attention of a wide circle of microscopists to this curious creature it may be sought for in other localities, and its history still further explained.

In conformity with the view adopted in the notice of the "Protean Animalcules" in the INTELLECTUAL OBSERVER for February of this year, Dr. Wallich expresses his belief that the Amabe, respectively named princeps, diffluens, and radiosa, are mere transitory phases of one and the same species, their dif

ferences being of shape rather than structure. With the new form, which he designates villosa, the case is altered by the constant presence of a particular organ not found in the other kinds, and which marks a decided advance in specialization. The organ in question consists of a tuft of villi, capable of varying in length and breadth, but never disappearing except as an optical result of the position the creature may assume. The aspect of the Amaba villosa may be seen from the accompanying drawings, and those hitherto observed are mostly larger than the better known kind, some of them "attaining a diameter of not less than of an inch."

Dr. Wallich originally discovered this species in Lower Bengal in ferruginous pools, and when rambling over Hampstead Heath, behind Jack Straw's Castle, his attention was excited by numerous pools and puddles of a similar kind, the sediment in which disclosed the form of his old Indian acquaintance. The pools in question contain much flocculent matter, apparently of vegetable origin, strongly coloured by peroxide of iron. At some seasons they exhibit little animal life, and I had been so often disappointed with them that at the very time when Dr. Wallich was collecting his specimens, I warned some brother collectors that they were of no use. I mention this fact to show the necessity of never giving up any situation as hopeless, unless it has been tried under all varieties of season and weather.

When I read Dr. Wallich's first paper I expressed my desire to see the new creature, and he was so obliging as to show me some of his own specimens, and to give me a few from his then waning stock. In March he found them plentiful, in April less so, and by May they became exceedingly scarce, and soon disappeared. When plentiful they were associated with diatoms, chiefly pinnularia, and swarms of Crumenulæ and other coloured members of the Monad family. Fine specimens presented a beautiful appearance from being crammed full of these objects of food, which preserved their natural colours, and glistened with brilliant tints of emerald green, and various shades of orange, red, and brown. The voracity of the animals was extraordinary; there seemed no other limit to their appetite than the capacity of their whole bodies to take in and hold the miscellaneous subjects of their choice. Those which I saw were not very active, being, as Dr. Wallich explained, far less so than others which he had previously obtained. Without any noticeable structural change they grew languid, put out a multitude of small thin pseudopodia from various parts of their bodies, and finally died. When in better health their pseudopodia, as seen by me, were always broad, moderately long, and with blunt rounded tips.