GEOLOGICAL CLASSIFICATION OF IRON ORES.

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The extent of this description of ore is not yet accurately defined. It has been found in several places in Northamptonshire, Lincolnshire, and southwards in Oxfordshire, Rutland and Dorset, northwards into Yorkshire; and probably it will eventually be found in other localities, including the great chalk formation.

In the Northampton ores a greater degree of irregularity in the yield of iron is observed in the following analyses of a very rich and a very poor ore :

The ores of this formation are largely developed in France, and the cheap rates at which they are mixed and cleaned have greatly contributed to the late extension of the iron industry of that country.

The Lias Formation.

The lias formation appears to be very deficient in iron ores. A few thin beds of earthy carbonates are known to exist, and have been partly worked in Lincolnshire and Yorkshire; but the existence of any continuous beds, containing a rich per-centage of iron, has not been made known.

In the marls constituting the upper series of the new red sandstone, magnetic iron-sand is found. The red sandstones and magnesian limestones contain nodules of hæmatitic concretions; iron pyrites, too, are common. With these exceptions, however, this system is destitute of iron ores.

Carboniferous System.

The iron-works of this country derive their principal supply from the earthy carbonates of the coal measures, which furnish, with proper treatment, crude iron of the best quality. The great coal-fields of South Wales, Staffordshire, Yorkshire, and Scotland, and the minor fields of Shropshire, North Wales, and Warwickshire, are abundantly supplied with these carbonates. The principal range of the carboniferous or mountain limestone, according to Mr. Warrington Smyth's recent report, emerges from beneath the Durham and Northumberland coal measures on the east; is bounded by a steep declivity, overlooking the river Eden on the west; reaches its culminating point on the long mountainous ridge of Cross Fell, thus forming the vast tract of moorland near Alston, and in the high desolate region adjoining the Scottish border. The mode of occurrence is in bands and nodules of a dark bluish-gray colour, dispersed through the shale. The bands vary greatly in thickness, from a quarter of an inch to two

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ORES OF THE CONTINENTAL COAL-FIELDS.

feet and upwards. The composition of the ores found in the Scotch field is well represented by the following analysis:—

Earthy carbonates from the other coal-fields are of a very similar character. The analysis of a specimen from the Warwickshire field is subjoined:

The coal-fields of the Continent appear to be less abundantly supplied with these ores, and the quantity found is exceedingly limited. In France the coal-fields of the Garde and the Loire yield small quantities to the adjacent works. The analysis of a specimen from the latter field shows a considerable difference in composition from the Scotch and Warwickshire ores; the per-centage of phosphoric acid seems excessive, while that of carbonate of iron is very low.

The Westphalian coal-fields contain numerous bands of earthy carbonates,

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ORES OF THE AMERICAN COAL-FIELDS.

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and probably at no distant day they will be used in conjunction with the mineral fuel with which they are surrounded. Limited quantities also are believed to exist in the Biscayan provinces of Spain.

The North American fields contain workable bands of these ores, which, though inferior in richness to similar ores in England, are used to a considerable extent in competition with the hæmatites from the older formation. Virginia, Kentucky, Tennessee, Alabama, Pennsylvania, and Ohio, possess large deposits in their coal formations; while Missouri and the other less perfectly explored states of the west are believed to contain equally important deposits. By analysis, one of the best specimens of the Pennsylvanian field gave :—

When oxidized, this ore forms hydrated oxides-brown or yellow hæmatites. In its original form, in the United States, it is found in round or flattened lumps, or spheroids, ranging from globules the size of a pea to masses of several tons weight, imbedded in clay, clay-slate, sandstone, shell, or limestone, and arranged in regular veins; but as there are often large masses of lead-slate between the balls, it is an expensive ore to work. The order contains about thirty-three per cent. of metal; when roasted, it emits the peculiar earthy odour incident to clay and clay ores.

The Carbonaceous Ores of the Coal Formations.

These occur extensively in some districts, but on the whole are much less abundant than the earthy carbonates. The coal-fields of Scotland contain the richest deposits hitherto discovered. North Staffordshire possesses valuable deposits, which are wrought to a large extent for the supply of local furnaces and transportation to South Staffordshire. South Wales also contains numerous seams of this ore, which are partially wrought in several places. Of late years, small quantities have been wrought in Ireland, and shipped to the Scotch works; but the extent of the deposits in that country is not yet ascertained.

The composition of a specimen of the Scotch carbonaceous ore (black band) is seen in the following results of an analysis by Dr. Colquhoun :

The North Staffordshire ore has a similar composition, as is seen by the results of an analysis by M. Herepath. Generally, however, these ores con tain notable quantities of phosphoric acid, and not unfrequently an amount of sulphur, even larger than is here represented under bisulphide of iron :

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Bituminous matter, water, carbonic acid, and loss 37-35

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The South Wales ores of this class are not generally rich. By analysis, a very clean specimen yielded: protoxide of iron, 43′92; protoxide of manganese, 480; alumina, 56; silica, 1.80; lime, 2.60; water, carbonic acid, and loss, 47°24=100 00. Ores of this class also exist in the Westphalian | fields, and to a limited extent in the French fields. They have also been dis covered in the State of Maryland.

The proximity of the ore to the fuel required for its reduction, and to the limestone used as a flux in the smelting furnace, has conferred on the several coal-fields such immeasurable advantages in the economical production of superior metal, that it is probable they will long continue to be the principal seats of the manufacture; more especially as, added to these advantages, an abundance of the finest fire-clays and refractory sandstones, as well as building stone of good quality, is generally found. It is thus seen that the great coal formations of this country contain, in an eminent degree, every material required in the manufacture of iron. The highly ferruginous character of several coal-fields is well exemplified in the following abstract of a section of the South Wales basin at Merthyr Tydvil, with the yield per acre of iron by the several descriptions of strata:

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In addition to the earthy carbonates and carbonaceous ores, the coalfields contain iron pyrites, which, though considered worthless, and productive of injury, even when used in the smallest quantity, may ultimately be found useful for the production of a species of crude cast-iron. This ore usually occurs in the coal as concretionary masses, but at other times it is found adhering to, and is disseminated amongst, the rocks of the lower measures. The composition of the masses from the coal seams is usually 48 parts of iron, with 52 of sulphur mixed with carbonaceous matter.

Carboniferous Formation.—The mountain limestone generally contains a small quantity of iron disseminated through its mass, as oxide or bisulphide. Particular coal fields also possess large deposits of rich hæmatite ore, of a quality adapted for the production of superior iron. From the mines of Whitehaven in Cumberland, and Ulverstone in Lancashire, large quantities of ore are mined and despatched to the ironworks of South Wales and Staffordshire. Gloucestershire also produces a considerable amount, while Glamorganshire, Derbyshire, and Scotland severally produce limited quantities of rich ore from the limestone measures. The carboniferous limestone of Northumberland produces a quantity of the carbonate of iron, which has recently received some attention from neighbouring smelters.

To the west, on the northern shoulder of Crossfell, and to the east at Kilhope and in Weardale, the outcrops of iron veins again present themselves. In the eastern part of this region the sparry ore makes its appearance abundantly. Here, as elsewhere in the neighbourhood of Stanhope Burn, in Weardale, the veins are particularly charged with this ore. Mr. Smyth gives the following analysis of a piece of this ore derived from the Rispey iron in Rookhope, remarking that the high character of the iron produced from similar ores on the Continent, more especially the steel-irons of Siegen, Styria, and Carinthia, render the introduction of this ore into the British iron manufacture a step of much importance :—