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The wider, however, the geological knowledge of the mining engineer, the better will he be able to cope with the difficulties that present themselves in his arduous calling. His services may not always be restricted to the same district. His advice may be sought in other districts, where there are other rocks, other successions, other dislocations and appearances, and he will be but poorly prepared to deal with these unless he is in some measure acquainted with the general principles of geology. Besides, new substances are yearly being utilised, and it is the duty of the mining engineer to keep pace with this progress, and to see that nothing in his workings be left unnoticed or unused. While every region of the globe is being ransacked to supply the mineral and metallic requirements of Europe and America, the mining engineer may safely calculate upon a wider field for his services-and these services can only be valuable and reliable in proportion to his scientific knowledge of the subjects with which he has to deal. Sinking shafts, driving drifts, pumping, and ventilation, are arts of prime importance; but where to sink, the nature of the minerals sought, their mode of occurrence, and the dislocations to which they may have been subjected, are of equal importance, and can only be known through some acquaintance with the science of geology.

But it is not alone to the farmer, the land agent, the builder, the civil engineer, or the mining engineer, that some acquaintance with geology is of importance. Its applications to the arts and manufactures are numerous and direct-to the fictile arts of the potter and glassmaker, to the manufacturer of mineral pigments and dyes, to the metallurgist and chemist, to the lapidary and jeweller, and even to the mechanical engineer and machinist. The potter and glassmaker derive all their clays and sands from the earth; all our mineral pigments are procured directly or indirectly from the same source; so likewise are all our metals, whether native or as ores; and so also our fossil fuels and lights; our millstones, grindstones, and whetstones; our salts and saline earths; our gems and precious stones. In fine, there are few of the arts and manufactures which do not less or more depend on the mineral and metallic treasures of the earth; and surely some acquaintance with the composition and structure of that earth, so that the place of those minerals and metals may be known, their abundance ascertained, and the facility of obtaining them be determined, cannot fail to be of advantage to those who have to fashion and fabricate them into objects whether of utility or ornament. It is not required of practical men to go deeply into the

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theories of geology, for that is impossible, and useless even if it were possible; but surely an intelligent acquaintance with the nature and origin of the materials they are daily manipulating cannot be otherwise than a gain, and a source of satisfaction even where the thought of pecuniary gain is altogether out of the question. Civilisation depends in a prime degree upon our mastery over the opposing forces of nature, and we cannot conquer any force or power save by the application of a superior one. Physically, man is weak and helpless; armed with implements and machinery he becomes a Titan. Without tools and machinery, man has to succumb to the forces of nature; equipped with these, they become his willing servants -turning his wheels, raising his weights, wielding his hammers, lessening his labours, and carrying him over land and sea with unparalleled celerity. Our most important implements and machinery are derived from the mineral world; the heat that sets them in motion is derived from the same exuberant source. How direct, then, our civilised dependence upon the earth and a knowledge of its mineral and metallic treasures! How important to every art and manufacture to learn something of the nature and character of the source from which they are procured!

To obtain this information, in a general way, is by no means a difficult task. It is not required of the practical operator that he should be learned in geological theories, in mineral species, or in paleontological discriminations. Enough for his purpose to understand the chronological succession of the rock-formations, to know the general character of the strata of which they are respectively composed, the changes these strata may have undergone, the areas over which they are spread, and the facilities with which any of their products can be obtained. The study of any recent text-book, the power to read aright geological maps and sections, and a knowledge of the composition of the peculiar products he has to deal with, are about all he requires for the prosecution of his task. Armed with this amount of knowledge, he will be enabled to conduct his operations with greater certainty, and be less liable to be led into visionary speculations and experiments. Acquainted with the wide and varied field of geological products, he will cease to abide by local and restricted supplies, while cheaper and more easily manipulated substances can be obtained from other regions.

To put the facts of Economic or Applied Geology plainly and methodically before the reader is the aim of the present treatise; and though each department may be studied separ

ately, a better knowledge of the subject will be gained by going over the whole, and especially by carefully reading the introductory chapters devoted to the general principles and classifications of the science. Understanding the chronological arrangement of the systems, and the general lithological character of the various formations, the practical operator will be in a much better position to understand the nature of the materials that come within the range of his own special department. Of course, it is only with the raw materials—their nature, position, and abundance-that the practical geologist has to deal. The moment they pass to the furnace, the retort, or the factory, they come under the domain of the metallurgist, the chemist, and fabricator, whose processes and appliances require other knowledge and other lines of research. It is true the geologist cannot be altogether indifferent to these processes and appliances; but, at the same time, it must be remembered that his special function is to discover the raw materials, to determine their positions and accompaniments, their abundance, and the facilities with which they may be procured; and generally, to arrange and classify them-be they mineral or metallic-so as to know their variety, their rarity, or their exuberance in the crust of the earth. Restricting himself to this function, the geologist can supply much valuable information, and this without at all infringing on the field of the technologist, whose methods are mainly of a chemical and mechanical nature.

II.

THE ROCKY CRUST.

I. ITS STRUCTURE AND COMPOSITION.

ALL the minerals and metals with which the arts and manufactures have to deal being obtained from the earth's crust, some knowledge of its structure and composition is indispensable to the economic geologist. For this reason we devote the present chapter to a brief outline of Geology; more especially as regards the physical characters of rocks and minerals, their modes of occurrence, and their chronological arrangement. With due attention any intelligent reader may easily make himself acquainted with these peculiarities; and the more intimate his knowledge, the better will he be enabled to understand the nature of the industrial products and processes that may come under review.

Stratified and Unstratified Rocks.

The exterior crust, which forms the theme of the geologist, is composed of rocks; and under this term are included all its substances, whether hard or soft, superficial or deep-seated -sands, sandstones, clays, shales, peats, coals, limestones, ironstones, lavas, basalts, granites. Whatever their mineral character, these rocks are found to occur in two main positions -stratified or bedded, and unstratified or eruptive. Reasoning from the manner in which rock-matter is deposited at the present day in lakes, estuaries, and seas, the stratified are regarded as of sedimentary or aqueous origin-that is, as having been formed through and by the agency of water. And reasoning, in like manner, from the ejectments of volcanoes, the unstratified are regarded as of eruptive or igneous originthat is, as having been formed through and by the agency of fire. In the accompanying illustration, the "Castle Rock" of Edinburgh is a truly eruptive or unstratified mass breaking through the sedimentary or stratified sandstones and shales

which are tilted up, and slope away from the centre of eruption. Wind-blown materials, as sand-dunes-chemical deposits, as calcareous tufa-and organic growths, like peat-moss and shell-beds-are usually classed with the stratified; while showers of volcanic ashes, and other irregular ejectments, though arranged more or less in layers, are described merely as stratiform. Generally speaking, the sedimentary rocks are formed from the waste and debris of pre-existing rocks, are lam

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Edinburgh Castle Rock:-Basaltic Clinkstone passing through Lower Carboniferous Shales and Sandstones.

inated or bedded in structure, comparatively soft and fragmentary in texture, and frequently imbed the remains of plants and animals. The eruptive rocks, on the other hand, however originating, make their appearance from below, are amorphous, or occasionally columnar, in structure, uniform and crystalline in texture, and rarely imbed any traces of organic remains. While the preceding are the general characteristics of the stratified and unstratified rocks, it must be borne in mind that there are many anomalous masses of conglomerate and breccia on the one hand, and curious sheet-like overflows and stratiform ash-beds on the other.

At the present day, stratified rocks are being laid down in all lakes, estuaries, and seas, and unstratified ejected from all volcanic centres. And as the forces (meteoric, aqueous, organic, chemical, and igneous) by which old rocks are wasted and new ones reconstructed from their debris, are as enduring as the planetary system from which they take their rise, the geologist is entitled to ascribe the formation of the rocky crust to the operation of similar agencies in former periods. In this

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