THE STRATIFIED OR SEDIMENTARY ORES.
By sedimentary ores we mean the stratified or bedded ores of the coal-fields, and those of the formations immediately preceding the coal measures. To this class belong the fossiliferous ores of Bloomsburg and the block ores of Danville, the stratified ores of Broad Top and Hollidaysburg, the "lenticular" ores of Western New York, the ores of the upper Susquehanna, and the "fibrous red oxides" of Tennessee and Alabama. The fossiliferous, "lenticular," and "fibrous" are red oxides, and exist principally in the "Surgent" series of Rogers. The ores of the Meridian formations succeeding are mostly brown oxides, and exist in thin layers imbedded in clay, and generally in contact with or in proximity to the limestones of that era. The ores of the "Cadent" and "Vergent" series are generally calcareous or fossiliferous,—but partake more of the red than the brown or hydrous character. All these beds of ore are thin, and not gene rally very productive; but they are widely distributed, and generally rich in metallic yield near their oxidized outcrops: they depreciate, however, when protected by heavy strata of impervious rock or slate from the action of frost and heat, water, wind, and sunshine. But below those influences these ores are lean, thin, and expensive to mine. The rich red oxide (fibrous) of Tennessee and Alabama lies on the face of the ridges, generally without covering, and always open to the influences of water, frost, and heat. But when not exposed to those influences, they are neither rich nor available, being lean, silicious, and hard. The process of deoxidization to which these ores have been sub. jected disintegrates and changes the structure of the mass, separating the particles of iron from the earthy matter, leaving the latter in dust or clay, and the former in con centrated mass.
This process is singular, but it is not confined to these beds alone. All stratified ores with which we are familiar, except the rich carbonaceous ores of the coal-fields, are subject to like influences when exposed on their outcrops or when concealed in the earth.
The calcareous ores of Johnstown, in Cambria county, now used so extensively at the Cambria Iron Works, were extremely rich at their oxidized outcrops, and yielded double their present percentage of metallic iron. The red oxides of Danville were rich and promising when first developed, and for a considerable distance under cover their yield was good and they were mined at a reasonable cost; but, on being followed below water-level and beyond the influences of the atmosphere, they became lean and thin, and are now abandoned as not available.
These ores are generally the result of precipitation in water, from the ferriferous material which it contained, either in solution, or as derived from volcanic eruptions. They are seldom or never rich in their normal condition, but exist simply as ferriferous strata, and only develop available ores when exposed to the chemical action of heat, water, or atmospheric influences.
These ferriferous beds exist throughout the Palaeozoic formations in every grade of richness from two or three to fifty per cent. of metallic iron. We find these strata out cropping everywhere in the anthracite regions; but, unfortunately, they seldom contain enough iron to become, through oxidization, available in the furnace. But many of the argillaceous and silicious ore-beds of the anthracite measures could be used with economy in the blast-furnace, if mined at available rates. By slow calcination or long exposure to the elements, the clay and silex disintegrate and the iron separates from these earthy impurities, leaving them generally in the form of dust or fine-grained powder, which, under a process of crushing and washing, can be entirely separated from the ore and with much economy in use.