Imagens das páginas

Quabtz Rock. (Syn. Quartz compact of Beudant.)

The quartz rock of the two colonies consists of two distinct varieties, the structure of which much differs, although appearing similar to the naked eye. The first variety is of a whitish or somewhat milky colour, at times translucent; it is free from foreign ingredients, and perfectly homogeneous. The second variety differs in colour and translucency, and shows, when examined with a lens, a granular structure, composed of concretions united into one mass by a paste perfectly similar to the grain: at times, as is the case at Dr. Hill's (Shoalhaven River, New South Wales), it presents the appearance of a jasperoid rock, with very indistinct concretions.

Localities.—The first variety is extensively developed about Bathurst, in Argyleshire, and on Mount Kosciuszko (New South Wales). In Van Diemen's Land, its most remarkable locality is the dividing range, west of Lake St. Clair, Frenchman's Cap, and the spur which unites that mountain to the main ridge of the dividing range, and which that quartz rock exclusively composes.

The granular variety is more generally diffused than the preceding one. In New South Wales, it is found in many places about the Upper Hunter, and particularly in Argyleshire, about Barber's Creek, Ajimatong Ridge, and Sharwin's Farm.

In Van Diemen's Land, it is principally found between the Meander and the Mersey rivers, at Rocky Cape, Cape Grimm, and the heads of the Derwent.

Remarks. — The first variety agrees in all its characteristics throughout the above-named localities, not only mineralogically, but also in its geological position and relation. This variety, in New South Wales, as well as in Van Diemen's Land, whenever it reposes upon granite proper, serves as base to mica slate.

The second variety shows evidences, both geological and mineralogical, of being posterior in date to the first. In most cases it forms the superstructure of the rocks belonging to the second epoch, under the account of which, allusion will be made to it.

Eurite (Syn. Feldspath grenu, Brard; Hatiy; Weisstein of Werner;)

Is composed entirely of felspar; sometimes aggregated in minute laminae, in which case it is susceptible of a mechanical division, parallel to the laminae; sometimes possessing a finely grained structure, and in such case exhibiting a conchoidal fracture; its colour is a pale yellowish red; it is inferior in hardness to quartz; adheres to the tongue, and exhales an argillaceous odour.

Localities. — It covers some portion of a granitic country about Wellington, and in the vale of the Clywd, and is also found on the summit of Flinder's Island. In Van Diemen's Land, it appears first between Mount Cameron and Waterhouse Point, and is next to be met with on the Black range. It is also found on the St. George's and Scamander rivers, to the north of St. Patrick and of Ben Nevis, and to the south of St. Valentine's Peak (Hampshire Hills).

Remarks. — This rock is seldom seen composing alone a tract of country. It is associated with granite; and frequently forms very large masses and veins conjoined with that rock, as is the case in the vale of Clywd, New South Wales.


Colour, sometimes emerald, sometimes leek green, but never uniform throughout; the mass displaying in small spots, irised hues. Externally, it often shines with a waxy or resinous lustre: at the edges, it is translucent. It is found in masses composing a cluster of mountains in Van Diemen's Land, known under the name of Asbestos Hills. It feels unctuous: the streak is generally of the same hue as the rock, though sometimes varying from a brighter to a duller shade. It is solid, semi-hard, and brittle: the fracture earthy, uneven, sometimes laminated; the fragments irregular and splintery. It is traversed by short, curved, and narrow veins of a white, silky amianthus, the fibres of which are perpendicular to the direction of the vein. It does not affect the magnetic needle.

Localities In New South Wales, serpentine is

found N.E. of Port Stephen, between Bathurst and Molong, and at a locality named Spring Hill; but the largest developement of this rock is in the range which lies between the Coodradigbee and Doomut rivers. It there presents beautiful specimens, approaching the character of precious serpentine, and containing fibrous talc and small fibres of amianthus. In Van Diemen's Land, the Asbestos Hills are the only locality where serpentine is seen in a mountainous mass. On the west side of those hills, it is associated with mica schist; on the east, with limestone; on the north, with greenstone. The maximum height at which it is found is 1500 feet: its structure is decidedly amorphous: but in the vicinity of the river Rubicon, it shows some slight appearances of stratification.


Mica Schist.

The difference in the colour of quartz and mica, and the varying proportions in which those minerals are aggregated, impart to mica slate an infinite variety of hues, including shades of green, white, red, blue, brown, and yellow. Its structure is distinctly slaty, yielding to the nail, and easily separating in thin layers. Sometimes the minute laminae of mica render it more compact, when its slaty structure becomes indistinct, and the fracture splintery, and often conchoidal: in this case it appears to the naked eye homogeneous, and resembles flinty slate. It is mostly vertical and contorted; closely fitting the waving lines of the crystalline base upon which it rests.

Localities.—In New South Wales, its range is very limited: on the eastern side of the mountains, it seems abraded; on the western, much broken and contorted. As far as I was able to ascertain, mica slate in New South Wales is only to be met with on Mount Kosciuszko and Mount Pinabar (Australian Alps).

In Van Diemen's Land, it is found between Point Eddystone and Mount Cameron; Piper's River and Miller's Bluff; Port Sorrel and Asbestos Hills; on the rivers Mersey and Forth, Rocky Cape, Black River, and Cape Grimm.

Remarks The varieties of mica slate found in the

two colonies have in a great measure resulted from the different circumstances under which the slates came in contact with the crystalline rocks. On Ben Lomond, mica slate was reduced to exfoliation, whenever it came into contact with greenstone. The same effect is observed in the mica slate of Piper's and the Mersey rivers. Its strata are in most cases vertical. It is associated with granite (Mount Cameron) ; with sienite (Mount Kosciuszko,Mount Pinnabar, and Point Eddystone); with serpentine (Asbestos Hills); with quartz rock (Frenchman's Cap and the western dividing range); and with diabase (Lake River, Scrubby Den).

Siliceous Slate

Is most usually grey, though sometimes white, reddish, or yellowish: it is also opaque; but in a few instances translucent at the edges. The fracture in small specimens is a little conchoidal. The mineral is traversed by numerous veins of quartz, looks greasy, and is tough.

Localities. — In New South Wales it is found at Munmurin Brook, Dart Brook, the River Karua, Booral, St. Patrick's Plains, Vale of Clywd, Fish River, Campbell River, Molong, Wellington, Gidley East, Ajimatong, and on Manes Range.

In Van Diemen's Land, on St. George's River, Mount Cameron, Little Forrester River, Patcham, Hampshire Hills, Emu Bay, Rocky Cape, Montague River, Cape Grimm, the Eldon Range, and River King.

Remarks The strata of siliceous slate occur for

the most part in a vertical position; at times, however, especially in flat or but slightly elevated countries, it is found very nearly horizontal, as on the river Karua. When in contact with crystalline rocks, it is seen usually associated with sienite, eurite, quartz rock, diabase, and porphyry. When in contact with slates, it rests on mica slate, and alternates with argillaceous slate. Its masses display distinct stratifications, composed of seams half an inch in thickness.

« AnteriorContinuar »