sandstone; he knows, also, that after the commencement of the new red sandstone, coal in workable beds ceases to be found, and that lignite, jet, and brown coal are mere local and insignificant deposits. Besides determining the position in which coal, ironstone, and other useful strata occur, geology can direct the miner through all those obstructions occasioned by faults, dykes, slips, and the like; for even these, irregular as they seem, bear certain evidence of their direction-upthrow or downthrow-which the experienced eye can readily detect. As with the minerals of commerce which occur in strata, so to a certain extent with the ores of lead, copper, tin, silver, and gold which are found in veins and lodes. These veins follow certain courses in relation to the great axis of elevation with which they are associated, are interrupted by cross dykes and veins, are thrown up or down by dislocations-all of which an experienced geologist can determine and map out, so as to save much fruitless waste of labour and capital. 330. The importance of geology to the civil engineer and architect is so obvious, that the fact requires little illustration. Possessed of a well-constructed lithological map, on which are delineated the various kinds of strata, their dip, direction, and other particulars, the engineer has a safer and cheaper guide for his direction than the scattered data of the boring rod. He sees at once the nature of the rocks through which his work has to pass-whether common road, railway, or canal; can estimate with certainty the expense of construction, and avail himself of minerals which he knows must lie in the vicinity; while one ignorant of geological truths would blindly pass by such advantages. In fixing a line of road or railway, the informed engineer will avail himself not only of facilities for present construction, but calculate, from his lithological knowledge of the district, for the future benefit of those concerned in the undertaking. In the case of canals, moreover, where retention of water is indispensable, the geologist can effectually aid in the selection of a route, by attending to the nature and dip of the strata, and to the fractures and dislocations to which they have been subjected. He is enabled, from his knowledge of the rocks and their positions, not only to prevent waste of water, but to select a route where fresh supplies can be readily obtained from below. As with roads and canals, so with tunnels, docks, Artesian wells, and other undertakings commonly intrusted to the civil engineer. It is true that such works may often be satisfactorily enough completed without the aid of geology, but undoubtedly a knowledge of its deductions will materially assist, by conferring a certainty and security on what would otherwise be a mere system of trial and error. The assistance which geology brings to the architect is not quite so obvious; as actual experiment is, after all, the best and only test of a rock's durability. However, by observing the effects of weather, water, and the like, on strata exposed in natural sections, he can readily determine as to their fitness for any particular structure. The amount of waste experienced by ancient buildings is also another safe and valid test; and it is the travelled geologist, and not the mere builder, who can point to the locality, nay, to the very stratum, whence the stones of these buildings were obtained. Thus, both directly and indirectly, the science is brought to bear upon architecture; a fact fully appreciated by the legislature in its appointment of a commission, composed in part of geologists, to determine the rock most suitable for the structure of the new houses of parliament. 331. The assistance which geology is calculated to confer on the science of agriculture, constitutes one of the most apparent features in its economical importance. All fertile soils consist of two classes of ingredients-organic and inorganic the former derived from the decomposition of animal and vegetable matter, the latter from the disintegration of the subsoil or rocks beneath. Without a certain proportion of organic matter, no soil can be fertile; but it is equally true, that without a due admixture of inorganic compounds, all attempts to improve it will be fruitless. These compounds are chiefly clay, lime, silicious earth, and magnesia, with certain salts of iron, manganese, potash, and soda-all of which are obtainable either from the igneous or sedimentary rocks, or from the superficial accumulations formed by their debris; and the farmer can at once effect a permanent improvement on his land by supplying the particular ingredient in which his soil may be deficient. To do this, however, he requires to know not only the composition of the most prevalent rocks, but also the precise spot which they occupy; in other words, he must be able to comprehend the language and delineations of a geological map of his own country. Besides this admixture of inorganic substances, there are other conditions necessary to fertility; namely, facilities for drainage, capability of retaining moisture, the innocuous nature of the subsoil, and power of absorbing and radiating caloric. Soil overlying trap and limestone requires less drainage than that covering the coal measures, saliferous marls, or wealden, because the former rocks are full of fissures and joints, while the latter are chiefly tenacious and unbroken clays. Again, land of itself dry and friable may be rendered wet by springs which arise along some line of dislocation. The farmer acquainted with the deductions of geology would cheaply lead off these springs at their source, while he who was ignorant would laboriously furrow-drain his whole field, and find, after all, that his was the less effectual method of the two. Such are mere indications of the assistance which geology is calculated to confer on agriculture an assistance very apt to be overrated, unless the farmer at the same time avail himself of the discoveries of chemistry and vegetable physiology. 332. It must not, however, be supposed that the science is of practical value only to the miner, engineer, architect, and agriculturist; every individual is liable to be more or less assisted by its deductions. The capitalist who speculates in land, the agent who effects sales, the statistician, traveller, and explorer, may all reap direct advantage from the same source. Take, for example, a case of emigration:-Two individuals, possessed of equal capital, set out, say to New Zealand or to the Far West of North America. The one ignorant of geology fixes upon a locality characterised by the beauty of its scenery and the fertility of its soil; the other skilled in the science decides upon a long-rejected lot, of bleak and barren aspect, but rich beneath in coal, limestone, iron, copper, or lead, which his geological knowledge at once enabled him to detect. The former pays a high price for his land, and yearly toils over it to reap therefrom a remunerating harvest; the latter obtains his despised territory for a mere trifle, makes his fortune in the course of a few years, and when roads and canals are constructed around him, re-sells his property for fifty times its original purchase-money. Such instances are by no means of rare occurrence. Even our own country can furnish examples where estates, sold under ignorance of their mineral value, brought only ten or twenty thousand pounds, for which, in less than a dozen years afterwards, an offer of ten times that amount was rejected. 333. The advantages resulting to civilised life from the cultivation of geology must be rendered sufficiently obvious even by the above hasty and imperfect outline; and yet it is scarcely half a century since it was recognised as a legitimate branch of natural science. Previous to that period it was obscured by absurd theories, which drew down upon it the imputation of being a visionary and dangerous pursuit; now, by the cautious industry of its cultivators, it is established as one of the most important of human acquirements. It is taught in our schools and colleges, disseminated by treatises and from lecture-rooms, and especially fostered by every enlightened government. Like most other sciences, it has still a wide field of research before it, many difficulties to overcome, and prejudices to remove; but, linked in connexion with all that is valuable and interesting to man, there is little apprehension for the successful attainment of its object-a complete physical history of the planet we inhabit. |