Felstones and porphyries, for building, causewaying, macadamising; and the latter occasionally for ornamental purposes. Leckstones, or granular trap-tuffs, for oven-soles, furnace-hearths, and similar uses. Precious stones, in geodes and drusy cavities, as rock-crystals, agate, carnelian, calcedony, jasper, olivine, &c. GRANITIC ROCKS. Granites and porphyritic stones, for building, for decoration, monumental monoliths, causeway-courses, kerbstones, road-metal, and kindred uses. Granite blocks, for grinding and crushing purposes. Felspathic or decomposing granites (Cornish stone), as an ingredient in porcelain manufacture. Syenites and syenitic granites, less abundant, but employed for similar purposes as the ordinary granites. Precious stones, as accessory minerals occurring in granite rocks -rock-crystal, amethyst, cairngorm, topaz, tourmaline, beryl, emerald, garnet, &c. Such is a brief summary of the economic products usually obtained from the respective geological systems, and especially as developed in the British Islands. Lithologically speaking, the strata of a system may vary considerably at different parts of its development, and in distant countries may be still more dissimilar. Notwithstanding these variations, which must ever be incidental to sedimentary deposits, there is always a certain amount of resemblance, and it is this resemblance which should lead to a search for the same products in the same chronological system. Take, for example, the Trias of England and the Trias of Germany. Although the muschelkalk of the latter has no equivalent in the former, yet the other members of the system-sandstones, rock-salts, gypsums, and saliferous marls are sufficiently alike to furnish the same kind of industrial products. Or take the coal-formations of Wales or of Nova Scotia. Although the limestones of the former be carbonates, and those of the latter magnesian and gypseous, yet all the other beds-sandstones, shales, fire-clays, coals, and ironstones-are so similar, that those from the one field might be mistaken for those from the other. The resemblance, or rather identity, of the unstratified or pyrogenous 1ocks is still more striking. The granites and syenites of Egypt and Norway, the basalts and greenstones of Scotland and Germany, and the lavas and tufas of Italy and the Sandwich Islands, are all but identical in composition; and the pro ducts obtained from any one of these groups in one region, may be sought for, with all but absolute certainty, in another. It is in this way that a systematic summary of economic substances becomes of use to the practical geologist; for whether surveying at home or abroad, he may naturally expect to find in the respective systems a certain similarity of available products. Not that there are not wide exceptions to this rule -the cretaceous system of England and the cretaceous system of North America, for example-but because it is useful to know that certain substances are characteristic of certain formations, where these formations are fully and typically developed. The practical geologist should have a higher aim, however, than merely searching for substances already known, and on which the arts and manufactures have stamped a certain value. This is of itself good and commendable, and will bring with it. its own reward; but he should at the same time endeavour to extend our knowledge by noting every rock, mineral, and ore that comes under his observation, examining its nature, and, in conjunction with the technologist, trying to discover in what way and how far it can be rendered available to the arts and industries. The utilisation within recent years, for instance, of the ironstones of Cleveland, the oil-shales of Scotland, and the phosphatic nodules of the greensand, with all the commercial and social consequences that have flowed and are flowing from them, are things which hold out the incentive to the careful inquirer of discoveries equally novel and equally remunerative. It is true the theoretic or scientific aspects of geology are replete with interest and attraction, and to many these form the bourne and boundary of their investigations; but it need not be necessarily so, for its practical or economic aspects are, though in another way, equally interesting and important. To trace the history of our planet through all her former aspects and mutations, is no doubt a high and inspiring theme; but science is never more exalted than when, following her legitimate functions, she stoops to administer to the wants of our common humanity. Whatever tends to increase man's mastery over the forces of nature extends his domain; whatever improves the physical conditions of human life, lengthens the lever of its intellectual and moral advancement; and thus the discovery of a new economic product is as important in its own way as the solution of a scientific problem. The scientific problem may interest only a few, and affect others remotely; the new product is a direct contribution to the general wealth and wellbeing of society. But while this cannot be gainsaid, the student, as he values his own intellectual life and growth, should never forget that the discovery of scientific truths stands on a higher platform than mere invention, or the application of these truths to industrial requirements. Both are good and necessary, and cannot be ignored; but without discovery invention is helpless. The one creates, the other only adapts. Commercially speaking, invention may bring rewards which discovery cannot supply; but without discovery invention would soon languish in hopeless stagnation. The one is the spirit of progress, the other merely the bodily members which that spirit animates and controls. INDEX. ABERDEEN granites, 61. Adits, in vein-mining, 149. Agates as ornamental stones, 86. Agriculture and geology, 32-49. Alabaster, gypseous and calcareous, 84. Alum, sources and preparation of, 234- Alumina, salts of, 233. "1 salts as manures, 47. Amygdaloid as an ornamental stone, 79. " analyses of, 165. Antimony, its ores and uses, 290. in medicine, 260. Apatite as a manure, 44. Apœnite, or Ransome's patent stone, 100. Aqueducts for canals, 115. Arbroath pavement, 110. Architecture and geology, 58-88. Arenaceous rocks, 18. Bauxite as an ore of aluminium, 290. coals as fuels, 162. shales, distillation of, 176. Blackband ironstone, 302. "1 cuttings through, 102. Bridge of Allan waters, 250. CADMIUM, its ores and uses, 293. Cæsium as a metal, 293. Cairngorms as precious stones, 275. Carbuncle as a precious stone, 274. Carnelians as precious stones, 278. Cements, various, 93, 95, 97. in medicine, 260. Chalk as a manure, 43- Chalks, drawing, various, 222. Chlorine in medicine, 260. Chromium, its ores and uses, 294. Chronological arrangements of formations, Cipolino marble, 82. Civil engineering and geology, 105-129. Clays we fabricate, 182. Clyde, improvement of, 120. Coal, produce of United Kingdom, 180. 11 British, analyses of, 164. Colours for glass or porcelain, 192. 11 for streets and roads, 98. walls, 98. Concretes, nature and preparation of, 98. Connemara serpentine, 80. Contra or counter veins, 147. Copal, subfossil gum, 322. Copper as a native metal, 287. its ores and uses, 295. 11 in medicine, 260. Copperas or sulphate of iron, 235. ་་ products, 323. Crocus, for polishing metals, 201. Crust, the rocky, nature and structure of, Cryolite as an ore of aluminium, 290. Cuttings and tunnellings for canals, 115. DALBEATTIE granite, 61. granite quarries, 134. Derbyshire sandstones and grits, 71. 1/ spar, for ornaments, 85. limestones, 73, 83. Devonshire granites, 61. marbles, 83. Diamond as a gem, 265. "1 for cutting and polishing, 204. Docks and harbours, construction of, 117. Dredging and widening of rivers, 120. Dyke and dyke-faults, 144. EARTHY springs, 246. Eclogite as an ornamental stone, 86. sandstones, 69. Elements, chemical, table of, 14. Embanking and warping lowlands, 121. 115. " and aqueducts for canals, Emery, nature and uses, 202. 11 wheels, 198. Enamels, glazes, and colours, 192. Engineering, civil, and geology, 105-129. FAULTS, illustrations of, 10. 11 various, in coal-fields, 146. Fire-clay and its manufacture, 208. 11 analyses of various, 209. Fluor-spar for ornaments, 85. Forest-growth and soils, 36. Forest marble, 84. Forfar flagstones, nature of, 110. Formation, stratified, arrangement of, 23. |