66

eties, such as c, d, and e, usually occur associated with surface accumulations, such as drift or peat. Cotta writes of Oolitic Brown Ore, that it Occurs in the form of layers in many formations." Bogiron Ore, and its sub-varieties, are due to the decomposition of iron ores (often pyrite or marcasite), or minerals, or rocks containing a large percentage of iron. Black Bog-iron Ore in general is rich in manganese, while the yellow and sparry subvarieties are respectively argillaceous and siliceous.

G. HEMATITE ROCK.-A granular or compact aggregate of hematite, with arenaceous or argillaceous matter; usually reddish in colour, but sometimes blackish or rich brown.

Varieties are-a. Red-iron Mould, or Red Ochre ; b. Reddle or Raddle; c. Sparry Red-iron stone; d. Specular Iron.

-

Of these varieties, the principal are a, b, and c, while d seems to be rather rarely a rock-mass. e. Topanhoacanga, or Moorshead Rock. This Brazil variety is found among the surface deposits, and consists of fragments of specular iron, micaceous iron, and magnetite in a ferruginous matrix. In this rock there are various accessories; even, on rare occasions, grains of native gold.

H. SPHEROSIDERYTE, or SPHEROSIDERITE, Clay-iron Stone. A crystalline aggregate of siderite combined with argillaceous and carbonaceous matter. Impure varieties are arenaceous.

Spherosideryte, or Clay-iron Stone, occurs in thin beds, layers, and nodules, in beds of clay, clunch, and shale. It is typical of the coal-measures, but

is also found associated with other rocks. An important Coal-measure variety, very rich in carbonaceous matter, is said by Bristow to be called Black-band. Some beds of the latter are so rich in carbon, that they can be burned by themselves, and might be classed among the coals.

I. MINERALS OCCURRING AS ROCKS.- Some minerals occur in subordinate masses interstratified with the sedimentary rocks; these, however, are not of very frequent occurrence, minerals in mass more often being found in veins, nodules, or irregular accumulations.

a. Asphalte [Gr. asphaltos], Bitumen, Mineral Pitch.-Colour brownish, blackish, or black; lustre like that of black pitch, odour bituminous, melts at from 90° to 100°, and burns with a bright flame.

Of this rock Dana writes: "Asphaltum belongs to rocks of no particular age; the most abundant deposits are superficial."

b. Pyrite occurs in thin beds, layers, and as nodules.

c. Cinnabar.-"Occurs in beds in slate-rock and shale, and rarely in granite or porphyry."

-Dana. This observer also states that this mineral occurs as rock-masses, both in unaltered and metamorphosed sedimentary rocks.

d. Boracite "occurs in beds of anhydryte, gypsum, and salt."-Dana.

e. Trona, "in North Africa, forming a rock which is even used for building purposes.'

-Cotta. f. Aragonite, with its subvariety Flosferri. "The

most common repositories of aragonite are beds of gypsum, and beds of iron ore (where it occurs in coralloidal forms, and is denominated Flosferri), basalt, and igneous rocks."-Dana.

g. Manganese Ores, generally in the older rocks, but also in surface deposits.

h. Rhodochrosite occurs generally in veins, but at Glendree, Clare, Ireland, it forms part of the surface-deposits.

i. Bole, in subordinate masses, in limestone. j. Opal, or Vitryte, in very subordinate masses. k. Fluorite, and 1. Barite, rarely found in beds or layers, often occur as gangue in mineral veins.

m. Ankerite, sometimes as an independent rock. n. Malachite, usually in veins.

o. Melanite, in small accumulations.

p. Galmey, or Calamine, as aggregates in dolomyte.

q. Zincite, r. Galenite, s. Stibnite, and t. Arsenopyrite, rarely occur as subordinate layers, but more generally in veins.

u. Sulphur, in concretions and layers, principally in marl and limestone, also in the vicinity of volcanoes.

v. Wavellite, in subordinate beds or layers. w. Chalcopyrite, usually in veins.

C. Rocks partly mechanically, partly chemically, and partly organically formed. These rocks are always more or less crystalline, and usually occur as subordinate beds, interstratified with sedimentary rocks, but not always.

A. LAMINATED or STRATIFIED COAL.-A more or less

fissile crystalline aggregate of carbonaceous

matter; arenaceous or argillaceous to a greater or less degree.

Most coals do not belong to the Subaqueous rocks; some, however, have been formed mechanically from carbonaceous matter, that was first denuded, and afterwards deposited in the sea, or other waters.

NOTE. At the present day the accumulation of mechanicallyformed coal can be observed. Wherever peat-bogs or even hard coal-beds are exposed to denudation, more especially to marine abrasion, they are gradually carried away to be deposited in seas, lakes, &c., forming stratified more or less arenaceous or argillaceous carbonaceous beds, which eventually must be indurated, forming a hard coal. Some of these deposits in the vicinity of the Irish coast are of considerable thickness.

Varieties area. Cannel Coal, a compact, semifissile coal; breaks with a semiconchoidal smooth fracture, with little or no lustre ; colour dull black or greyish black.

Cannel Coal is bituminous and often caking. Of it Dana writes: "On distillation it affords, after drying, 40 to 66 of volatile matter, and the material volatilized includes a large proportion of burning and lubricating oils. It graduates into oil-producing coaly shales, the more compact of which it much resembles."

NOTE.-Some varieties of anthracyte have erroneously been classed as Cannel coal, on account of their smooth, close texture.

Subvarieties are-(a.) Parrot Coal, (b.) Horn Coal.

A Scotch subvariety is called Parrot Coal, because it burns with a crackling noise; while a Welsh is named Horn Coal, as it emits, when burning, an odour like that of burnt horn. An earthy subvariety is called, in Yorkshire, Clod.

And (c.) Torbanyte, Boghead Cannel, Boghead Mineral (after Torbane Hill, Scotland).-A dark brown variety of cannel coal; yellowish streak, without lustre, and having a subconchoidal fracture.

Torbanyte yields over 60 per cent. of volatile matter, and is used for the production of burning and lubricating oils, paraffin, and illuminating gas. b. Splint Coal, Splent Coal.-A hard, laminated, bituminous coal; not easily broken or kindled, though, when lighted, it affords a clear, lasting fire.

66

According to Page, the name 'Splint" or Splent," is derived from the coal splitting (or splenting) up "in large flaggy or board-like laminæ.'

وو

c. Culm, a fissile, flaggy, shaly, flaky, or scaly variety of non-bituminous coal or Anthracyte.

Culm sometimes occurs in independent beds, but more often it is found associated with Anthracyte. The flaky or scaly nature of some culm may possibly be due to the growth and decay of organic matter in layers, but in others undoubtedly it is due to carbonaceous matter having been deposited in

water.

d. Bituminous Shale, and e. Carbonaceous Shale. -Respectively bituminous or non-bituminous shaly aggregates of coal, clay, sand, and such-like; more or less crystalline; colour black, or blackish-brown.

Both the bituminous and carbonaceous shales graduate on the one hand into argillaceous shale, and on the other into coal. The former merges