In attempting any classification of Iron ores which shall be regulated by the conditions under which they are found, we are at once met with the difficulty of finding many similar varieties of ores occurring in lodes or veins, and also amongst those which are evidently sedimentary deposits. It will not, therefore, be attempted. There can be no doubt that the most ancient of the Iron formations are those Oxides of Iron which occur as lodes or veins in the slate and granite rocks. Of this kind we have some examples in Cornwall, Devonshire, Wales, and Scotland. Generally speaking, however, these veins are not sufficiently extensive to be worked. The Iron Mine at Restormel, near Lostwithiel, in Cornwall, which has been wrought for many years, and which still produces considerable quantities of ore, and those near St. Austell, in the same county, are amongst the most remarkable. At Hennock, on Dartmoor, there occurs an immense vein of Micaceous Iron ore, but this of late years has not been employed. All these are evidently the result of the aggregation of ferruginous particles, often under the influence of crystallogenic force, mechanically separated from water holding iron in solution, which has flowed through the rock fissures probably within a limited period after the formation of those fissures. The Iron lodes differ in no respect from those of the other metals, except in the nature of their contents, and they have been formed under analogous conditions, all of them indicating the influences of an elevated temperature, of an electrical disposing power, and those mechanical agencies which are still obscure, but which are being gradually developed under the general appellation of Osmose forces.

Magnetic Iron Ores.-Magnetic Oxide of Iron or Magnetite is a compound ore of the Sesquioxide of Iron and the Protoxide of Iron. Amongst other adventitious matters, this ore usually contains manganese and sometimes tin. In Western England several lodes of magnetite are known, one near Penryn and another not far from St. Austell, in Cornwall, has been worked, but not extensively. Near the Haytor rocks, on Dartmoor, a much more extensive deposit of this ore is found; but it is difficult in this case to determine satisfactorily, whether this is a set of veins or of beds interstratified with slate and sheeted masses of greenstone porphyry. At Brent, which is only a few miles distant from the Dartmoor deposit, we find magnetic ore covering, like a shell, an immense boss of trappean rock. In nearly all cases, magnetite is associated with, or is found in proximity to, some igneous rock, and to the action of this on either Oxide or Carbonate of Iron is no doubt due the magnetic character which distinguishes this ore. If the Spathic Carbonate is exposed to a regulated heat, it is converted into a Magnetic Oxide of Iron, and manufactories have been established for its production, to be used as a paint for work which is much exposed to the action of the weather.

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18

In attempting any classification of Iron ores which shall be regulated by the conditions under which they are found, we are at once met with the difficulty of finding many similar varieties of ores occurring in lodes or veins, and also amongst those which are evidently sedimentary deposits. It will not, therefore, be attempted. There can be no doubt that the most ancient of the Iron formations are those Oxides of Iron which occur as lodes or veins in the slate and granite rocks. Of this kind we have some examples in Cornwall, Devonshire, Wales, and Scotland. Generally speaking, however, these veins are not sufficiently extensive to be worked. The Iron Mine at Restormel, near Lostwithiel, in Cornwall, which has been wrought for many years, and which still produces considerable quantities of ore, and those near St. Austell, in the same county, are amongst the most remarkable. At Hennock, on Dartmoor, there occurs an immense vein of Micaceous Iron ore, but this of late years has not been employed. All these are evidently the result of the aggregation of ferruginous particles, often under the influence of crystallogenic force, mechanically separated from water holding iron in solution, which has flowed through the rock fissures probably within a limited period after the formation of those fissures. The Iron lodes differ in no respect from those of the other metals, except in the nature of their contents, and they have been formed under analogous conditions, all of them indicating the influences of an elevated temperature, of an electrical disposing power, and those mechanical agencies which are still obscure, but which are being gradually developed under the general appellation of Osmose forces.

Magnetic Iron Ores.-Magnetic Oxide of Iron or Magnetite is a compound ore of the Sesquioxide of Iron and the Protoxide of Iron. Amongst other adventitious matters, this ore_usually contains manganese and sometimes tin. In Western England several lodes of magnetite are known, one near Penryn and another not far from St. Austell, in Cornwall, has been worked, but not extensively. Near the Haytor rocks, on Dartmoor, a much more extensive deposit of this ore is found; but it is difficult in this case to determine satisfactorily, whether this is a set of veins or of beds interstratified with slate and sheeted masses of greenstone porphyry. At Brent, which is only a few miles distant from the Dartmoor deposit, we find magnetic ore covering, like a shell, an immense boss of trappean rock. In nearly all cases, magnetite is associated with, or is found in proximity to, some igneous rock, and to the action of this on either Oxide or Carbonate of Iron is no doubt due the magnetic character which distinguishes this ore. If the Spathic Carbonate is exposed to a regulated heat, it is converted into a Magnetic Oxide of Iron, and manufactories have been established for its production, to be used as a paint for work which is much exposed to the action of the weather.

A curious mass of Magnetic Iron ore occurred at Rosedale, in Yorkshire. The first discovery of this deposit of Iron-stone was at a quarry on the south-west side of the valley of Rosedale, about a mile south from Rosedale Abbey. When this quarry was opened out, it was found apparently to consist of a confused mass of ironstone boulders, of an ellipsoidal structure, often three or four feet in diameter. The interior of these boulders was generally blue, and comprised a solid dark oolitic iron ore, with, in many cases, sandy and solid crusts around it; and in receding from the centre the iron ore became paler, alternating with dark-brown purplish layers. Those variations did not occur where the iron-stone was covered by other strata, and the magnetic property proved to be most decided where the mass was the thickest. These circumstances appear to indicate that this mass was at one time in the state of a Carbonate of the Protoxide of Iron, not very unlike that which occurs in the Cleveland Hills, but that it had been exposed to influences-not necessarily calorific-by which the chemical change into Magnetite had been effected. This ore especially resembles the hydrated Magnetic Oxide of Iron, which can be obtained as a precipitate from an aqueous solution. Figures 1 and 2 in the Plate will explain more fully than any words the peculiar conditions of this remarkable and valuable Iron ore formation. The first section is by the late Mr. Nicholas Wood, the second by Mr. Bewick. It should be noted that the latter observer, writing of this deposit, says, "The Iron ore of Rosedale, instead of being a large mineral field, as was first asserted, and still believed to be so by many, is nothing more than a volcanic dyke; and the iron-stone opened out in this locality is not, as it is reputed to be, the main seam now being worked in Cleveland and Grosmont." The Magnetic Oxide of Iron has been discovered in Banffshire, Aberdeenshire, the Shetland Islands, and the Hebrides. It occurs also in Antrim, in Wicklow, and especially in the Mourne Mountains.

Red Hematite.-The deposits of this valuable ore—an anhydrous Sesquioxide of Iron,-which are found in Furness near Ulverstone, and near Whitehaven, are deserving of the closest attention. At Whitehaven, this ore is found in the carboniferous limestone and millstone grit (locally called "Whirlstone") near the outcrop or surface edges of the slaty rocks upon which these formations rest. Fig. 3 shows the mode of occurrence. At Todholes, where this ore was worked as a quarry, the bed had a thickness of twenty feet, and at the Park Mines a thickness of seventy feet of solid Hæmatite occurred.

The Ulverstone ore differs in physical condition from those of Whitehaven. Much of it is equally compact with the Cumberland ore, and this is known as "blast "ore; but the major portion occurs as a less coherent aggregate of exceedingly fine filmy scales of mica

VOL. V.

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ceous iron. In the Whitehaven district the ore is found filling cavernous spaces, which had evidently been formed in the limestone previously to the deposit of the Iron; these caverns being probably due to the action of water charged with carbonic acid, which readily dissolved a certain proportion of the limestone. In the Low Furness district, at Rickett Hills, and Mousell, the Hæmatite is found in lake-like deposits, which have been well described as "dish-shaped." These dishes of ore run from fifty to sixty yards in width, and are usually from eighteen to twenty feet deep. At Roanhead the ore is found in two basins, which are slightly connected with each other, but they have nothing of the character of a mineral lode. These basins are covered generally with sea-sand, which is often overlaid with a tenaceous clay. Nothing like a mineral lode occurs either at Whitehaven or at Ulverstone. At Stainton, a chasm worked open to day was long looked upon as a vein of ore, but the full exploration of it proved the contrary. Fig. 4 is a section of this chasm, which was worked altogether to the depth of sixty yards. The stone arch shown was built to support the walls of the fissure, it being thought that the ore would be found to a considerable depth below. Within a short distance a bed of clay, locally called "blue hunger," came in, below which there was not a trace of Iron ore.

Brown Hæmatite.-The Forest of Dean may be regarded as the chief locality for this variety of Iron ore, about 150,000 tons being raised annually. The Forest of Dean ores are commercially classified into Brush Ore, containing 90 per cent. of Sesquioxide of Iron; Smith Mine giving 89 per cent., and Clod or Grey Vein about 50 per cent. These iron ores occur under much the same circumstances as the Red Hæmatites of Whitehaven. The ironstone formation is immediately overlaid by the " Whitehead Limestone," a regularly stratified rock, the beds of which are often highly crystalline. This limestone is locally called "crease," and is traversed by innumerable small joints, which appear to have arisen from a shrinking, probably during the consolidation of the mass. The worked-out spaces in the " Mine Measures," that is,—the ironstone beds which have an average thickness of twenty-five yards,— are so extensive that they have been compared to the crypt of a cathedral. These prove the deposit to have taken place in caverns which had been previously formed by the removal of the limestone. There are many curious phenomena connected with the Iron ore formations of the Forest of Dean, which demand a careful examination. It is not, however, possible in this place to give the required consideration to those, since the space which can be allowed to this article is fully occupied, with the general review of our iron-stone deposits, and remarks on the conditions under which they appear to have been formed.

Some valuable deposits Lave been recently worked in Gla