The tonnage of coal raised in the United Kingdom in 1895 was 189,652,562.

It may be useful to refer to the mode of occurrence of some of the more important minerals.

Coal has already been mentioned.

Fire-clay is a species of indurated clay. It is found as a stratified bed; it is particularly abundant in the coal measures. As a rule, a bed of fire-clay has a seam of coal overlying it, but the coal may be very thin and of no present commercial value, or may be represented by a carbonaceous shale. Fire-clay is like ordinary surface clay in this respect, that it has no lines of bedding or stratification except where it joins another stratum; nor has it any cleavage, although it has joints along which it can be broken. To be valuable it must be nearly a pure silicate of alumina, mixed sometimes with silica. Fire-clays are seldom worked unless the bed is 2 feet or more in thickness. From 2 to 4 feet is a common thickness for a valuable bed of fire-clay. In some cases there are fire-clays 30 feet in thickness.

Ganister is an unlaminated sandstone. It is nearly pure silica. It often, if not generally, underlies a seam of coal, and is underlaid by fire-clay. It is very hard, and has been often used for road-mending; it is used for making fire-bricks capable of resisting great heat, and also for lining the "holes" in steelsmelting-works. A bed of ganister generally varies in thickness in a short distance from 2 or 3 inches up to 3 or 4 feet.

Gypsum, a white rock used for making plaster of Paris, is found interstratified with the marls of the Keuper formation. The beds vary from a few inches up to about 12 feet in English mines.

Oil shale is found in the Coal Measures of Great Britain, interstratified with other shales and seams of coal. It contains a great deal of petroleum, which is obtained by distillation. It is often got in coal-mining when it happens to be contiguous to a coal-seam; occasionally, as in the case of the celebrated boghead mineral in Scotland, it is worked by itself.

Phosphate of lime, in the shape called coprolites, in England, is excavated in parts of Hertfordshire and Bedfordshire, where it is found, at a little depth below the surface, in some parts of the Cretaceous formation. It is not found in continuous beds, but in hollows or troughs perhaps 7 or 8 feet in depth, which can be easily got with a pick, like a bed of pebbles, and appears to consist of fossilized animal remains such as sharks, etc. In Florida and Carolina it is largely excavated, sometimes in very dry ground, and sometimes dredged from rivers, where it is found in beds. In Carolina the beds are thin, usually from 8

to 18 inches in thickness, though they are occasionally thicker, In Canada phosphates are mined in veins of great thickness.

Red MarlRock

FIG. 35-Section of salt-mine and

strata.

Salt, like gypsum, is a rock, found interstratified with the red shales of the Keuper formation. In the mines of Northwich it is found in beds which attain a thickness of 50 yards (see Fig. 35); in some places, as at Wielitzka, near Cracow, the thickness is upwards. of 1000 feet.

Slates are indurated shales. In Great Britain they are generally met with in the Silurian and Cambrian formations. They have been greatly altered by pressure SO as to lose the nature and appearance of shale. The valuable slates are those which possess a suitable cleavage for splitting up into roofing-slates. Some of the finer varieties are exceedingly fissile, and an expert workman can split a slab 1 inch in thickness into upwards of thirty full-sized roofing-slates. The seams sometimes attain a great thickness-upwards of 800 feet; and they are often inclined at a very steep angle.

Stone. This is sometimes a stratified rock, as, for instance, Portland, Bath, and other limestones; Whatstandwell (Derbyshire), Bramley Fall (Yorkshire), and other sandstones.

The stratified rocks are sometimes worked by underground mining, as in the neighbourhood of Bath, but as a general rule stone is got by open work.

FIG. 36.-Section showing deposit of hæmaa, hæmatite; b, carboniferous

tite ore. limestone.

A great deal of stone is unstratified rock of the class commonly called igneous, such as granite, syenite, whinstone. Generally the granite is an intrusive mass, or is in a cone, round which have been deposited more recent rocks. This kind of stone is largely

got, both for building and road-making, by open work.

Occurrence of Metals.-Iron is the most important metal

got either in Great Britain or elsewhere.

1 C. C. Hoyer Millar.

It is generally found in the stratified rocks, and to some extent in all, or nearly all, the formations from the most recent to the earliest metamorphic formations.

It is most commonly found as a stone strongly impregnated with iron, and as such is itself a stratified rock. It is also found in great masses of more or less pure oxide of iron filling up cavities in rocks of much older date than the iron ore therein deposited (see Fig. 36).

The chief beds of stratified ore now worked in Great Britain are those of the Oolite and Lias and of the Coal Measures. Till within the last forty years or later, the Coal Measures afforded the chief supply of iron ore after the abandonment of the Sussex workings (Cretaceous rocks).

Iron ore is found abundantly in most of the British coal-fields, with the excep

a

b

с

3.6 Ironstone 8

7.6"

FIG. 37.-Section showing coal-measure ironstone. a, shale with black-bed ironstone; b, black-bed coal; c, seat earth.

tion of those of Durham and Northumberland.

The ironstone of the Coal Measures is found as a bed of hard stone, sometimes reaching a thickness of upwards of 9 feet. Generally it is much thinner, the stone being found in thin beds I inch and up to 6 inches in thickness, interstratified with shale (see Fig. 37).

The ironstone is often found as nodules or balls lying close together in regular layers in the shale.

If beds of ironstone of good quality happen to lie in close proximity to a seam of coal, they are often got in the same working, where the cost of working either separately would have been too great.

When thus associated with a seam of coal, the total thickness of ironstone got in one working is sometimes as little as 3 or 4 inches. When the ironstone is got by itself, at least twice that thickness of good iron ore in a total thickness of ore and shale amounting to 3 feet is necessary for profitable working. But these observations as to the profitable working of coalmeasure ironstone apply rather to a period of thirty years ago than to the present day. At the present date coal-measure ironstone can only be profitably worked in a few places where it is of exceptional excellence or great thickness, as, for instance, the Blackband iron ore of Lanarkshire; the ironstone of North Staffordshire, worked in a bed 4 feet in thickness; the Blackbed ironstone found near Leeds, which is worked as thin as

4 inches, together with a seam of coal 18 inches thick (see Fig. 37). With these and perhaps a few other exceptions, the coal-measure ironstones, which recently were the chief source of our ironsupplies, are now entirely unworked.

The iron ore of the Lower Oolite has taken the place of the coal-measure ironstone, because it lies near the surface (see Fig. 38), as in Northamptonshire, Leicestershire, Rutlandshire, and Lincolnshire, and is got by open work at about one-fourth of the cost of getting coal-measure ironstone; or else, as in Cleveland, it lies in a bed 9 to 12 feet in thickness, and being also softer than coal-measure ironstone, it can be got by underground mining at about one-third the cost.

a n

a

с

FIG. 38.-Stratified iron ore. o, Oolite limestone; a, ironstone; c, Lias clay.

The other chief sources of iron ore are the masses of red hæmatite found in Cumberland and North Lancashire, and of brown hæmatite in the Forest of Dean and South Wales.

Another oxide (göthite) has been got at a mine near Lostwithiel, in Cornwall. Ore has been found in other places, but out of 2,472,536 tons of hæmatite ore got in Britain in 1891, 2,394,990 tons were got in Cumberland and North Lancashire. The ore in these counties is found in great masses in the Carboniferous (mountain) limestone, measuring in some cases over 1000 feet long, by 750 feet wide and over 400 feet deep, and in other cases in veins 3000 feet long and yo feet wide. Sometimes the ironstone appears at the surface, but it is often completely buried beneath limestone rocks. It would seem as if the ore had been deposited in caverns formed in the limestone. larger deposits of ore are sometimes connected by narrow channels filled with ore.

The

Tin ore comes next to iron in importance amongst the metals raised in Great Britain. Nearly all the British tin-mines are in Cornwall, with slight exception in contiguous parts of Devonshire. Tin is found in veins, in the granite and killas (the latter being a metamorphic clay slate). The veins vary in thickness from a few inches up to 25 feet; in depth they have not been proved, the deepest mine being less than 1000 yards in depth. They are sometimes nearly vertical, and sometimes slope at an angle of 27° from the vertical. Occasionally the veins spread out horizontally into flats. Tin ore is an oxide of tin called cassiterite. Cassiterite is mixed with stone (generally chiefly composed of quartz), forming a rock. At Dolcoath

the tin rock is called "blue capel;" it is one of the hardest rocks known. Sometimes, as in the neighbourhood of St. Austell, the vein stone is soft. The ore is sometimes diffused through a large mass of rocks on each side of the vein or leader forming what are called stockworks, as at Carn Brea.

Next to iron, lead is the most widely diffused metal which is mined in this country. It is found in England, Wales, Scotland, Ireland, and the Isle of Man. It occurs in veins, chiefly in the Carboniferous limestone, as in Northumberland, Durham, Yorkshire, Derbyshire, and Flintshire; but there are also lead-veins in the Silurian, as in Mid-Wales, and in other rocks.

The principal ore of lead found in this country is galena, a sulphide of lead. The veins vary in width from a thin leader barely visible to the width of a large cave, say 20 feet. The vein is sometimes full of galena, and often it chiefly contains vein-stuff, that is, spar or other waste material.

The ores of copper, zinc, and barytes also occur in veins, like tin and lead, but they are only produced in small quantities in Great Britain.

English copper was at one time more extensively worked than it is at present, but the price that now rules is hardly sufficient to keep the British mines at work. The production in 1891 was 720 tons of metallic copper, while in 1863 it was 14,247 tons, or nearly twenty times the present output. But in 1863 the average value was £100 a ton, whereas in 1891 it was about £56 a ton. Owing to this low price, most of the British mines have been closed. It may be that at some future date British copper-mines will again be largely wrought. Mines are often closed owing to temporary difficulties which might be overcome if there was a substantial reserve fund with which to carry on the mine during times when the more profitable portions of the veins are exhausted, and it becomes necessary to make further explorations in search of rich deposits. In many cases the profits in good years are paid away to the shareholders, who may be a rapidly changing body, so that when the mine is temporarily less productive, during a period of low prices, there is no fund at hand with which to carry it on. The pumping of the water is often a constant and heavy charge, which cannot be borne by a mine having only a small output. Possibly at some future time, by means of the collective action of the community, the cost of water-pumping will be better distributed, and the total cost reduced in some cases by adits on a low level; improved machinery may be erected for winding, for