CHAPTER XL

MINERALS.

THE NATURE OF MINERALS—THEIR ORIGIN—THE METALS-IRON, ITS OXIDES, ITS ORES, ITS AFFINITIES, ITS USES-ALUMINA-ALUMINOUS GEMS OTHER ALUMINOUS MINERALS

CLAY-SILICIOUS MINERALS

-CALCAREOUS MINERALS-RECIPROCATION OF MATTER BETWEEN MINERALS AND LIVING BEINGS-THE CONTRAST BETWEEN INORGANIC AND ORGANIC THINGS IN REGARD TO LIFE.

MINERALS are substances which have no cells or other characters of organisation. They are governed entirely by chemical laws, without any modifying influence from a vital force. Most exist in the shape of crystals; and many are constantly in the course of formation, and increase by processes of crystallisation. But none, in the proper sense of the words, have any capacity of reproduction or growth.

A few, such as saltpetre, several constituents of soils, and perhaps the remarkable substance called amber, are formed by the chemical recombination of elements let loose from the decay of recent organic remains. Some, such as natron and the contents of spar caves, are formed by the solidification of dissolved saline matters contained in cold water. And many, such as sulphur, bitumen, and the deposits of hot springs, are thrown up from the depths of the earth to its surface, either directly or indirectly, by volcanic action. But the grand bulk of them are results of

ancient crystallisations beneath the hot seas of longago epochs; and are either constituents of existing rocks, or constituents of debris, detritus, soils, and other substances which have accrued from the disintegration of rocks. Many of these, perhaps, exist now in the same crystals as at their creation, or were formed by primal combination of their elements. But some, such as the several kinds of coal, were formed mainly out of dead plants; and others, such as coprolites, coral rocks, molluscous limestones, and animalcular segregations, were formed either through the instrumentality of animals or out of their remains. All the aboriginal ones, too, seem to have been put into their eventual position by the agencies which formed rocks or altered them; for several and sometimes many kinds of them lie intermixed in even the crystalline rocks, and all the metals occur in situations and connections widely different from those in which the very agencies of primal rock-formation themselves would have placed them.

The case of metals, indeed, is a very curious and most instructive one; and has been well stated, as follows, by Dr King:"They are found in mineral veins filling up fissures of rocks. These rocks are of all sorts igneous and aqueous-more ancient and less ancient. The metals themselves are met with in great varieties of condition, now one only in a chink, now several, now each by itself, now mingled together; here diffused through stone, there constituting an ore, and in a third instance forming detached lumps. Great difficulty has been experienced in accounting for the phenomena of these veins, as neither fire nor water, the two great agents in nature, possesses powers

equal to the results. 'That many veins,' says Dr Macculloch, 'have a double origin, is only one of the numerous difficulties that beset this subject.' Of late it has been shown in a very decisive manner by Becquerel, that electrical action can produce such effects. The experiments of Fox indicate the same truth. Without entering into the controversies which have been agitated on the subject, or attempting to clear up its remaining mysteries, three facts I may state, on the authority of eminent geologists, as now well established: First, the rocks had originally no such veins. Second, the cavities in which the metals collect were caused by disturbance and dislocation; and here we have another of the many benefits attending on those convulsions of nature which appear so formidable. Third, the metals were separated from the general mass of the rocks, and deposited in the chinks provided for them, by very slow and imperfectly understood processes. What a laboratory then was here! what multiplicity and immensity of chemical operations! To outward view, the mountain would have seemed a slumbering and inert heap of matter, when all of it was passing, from its pinnacles to its foundations, from its surface to its centre, through busy transformations. The infiltrated water was permeating every pore; so were the gases which that water absorbed, while the electric stream, flowing with ceaseless constancy and resistless power, impressed its influence upon all; and thus were the metallic particles disengaged from their earthy alliances, and conducted through their narrow and secret passages to their appointed store-chamber. And now when enlightened industry lays that chamber open to the light, the miner has little to do but

gather up the metallic treasures prepared to his hand!"

Iron is the most abundant of the metals; and may be selected as a grand specimen, not of them only, but of all minerals. It abounds in almost every part of the world; and exists under a multitude of aspects and in multitudes of combinations. It has powerful chemical affinities, and seems ever to have exerted them in the course of the world's changes; so that it occurs in all sorts of positions, and under the most startling diversities and contrarieties of form. It is the cement of many rocks, the colouring principle of most lands, and the body or basis of not fewer than about sixty compound minerals, and also an element in hundreds of others. It occurs in rock veins, in rock strata, in rock masses, in soils, in marshes, in springs, in animalcular deposits, in living plants, and in living animals. Many a man has more iron in him than he dreams of; for it exists largely in his blood.

Iron has such a passion for oxygen, that wherever it gets access to air and moisture it takes oxygen out of them, and forms the powder popularly called rust. But that powder, according to the different proportions of oxygen taken up, is variously yellowish, brownish, reddish, and blackish. Hence the colours of the greater number of soils and rocks; and hence the changes in these colours a little after the soils are ploughed up and the rocks are broken. Hence, too, the accumulations of the pigment powders popularly called ochres. But the combining greed of iron, and especially its greed for oxygen, have occasioned nearly all of it to pass from its original condition. Exceedingly little uncombined iron can now be found; so

little, indeed, as to be matter of high curiosity; and even that little, of course, cannot easily be kept from becoming less by rusting. Yet there is a remarkable exception. This occurs in the star-stones-the projected masses from other worlds to ours-of which we made some mention in our first and second chapters. All these contain uncombined iron; and the largest contain little else. And this iron differs much from the iron of the earth. It often has traces of cobalt, and always is mixed with from three to twelve per cent. of nickel-metals which never occur in connection with terrestrial iron; and it has a granular structure and silver-white colour, and can easily be cut with a knife, and is flexible and perfectly malleable without any aid from heat, and is not nearly so liable to rust as terrestrial iron. Some masses of it have external markings similar to the impressions made on a soft plastic body by hands and feet.

Iron ores are mineral combinations very rich in iron; and iron mines are immense quantities of some one or other of these ores in juxtaposition with substances which can be used to drive the iron out of combination, such as timber or coal to serve as fuel, and limestone to serve as flux. And no slight proof of the beneficence of God, and of the prospective adaptation of the earth throughout all its epochs of change to the present circumstances of mankind, is afforded by such juxtaposition. The ore and the coal and the lime were formed in ways widely different from one another, and at periods far remote from one another the first perhaps fitfully and by a series of electric processes, the second rapidly and by the amassing and baking of a world of vegetables, the third