GEOLOGICAL SURVEY

U. &., a bureau in the Department of the Interior, whose work it is to cla ify the public lands of the United States according to their geological character. The work of the Survey may be divided into three separate phases; geology proper, which has to do with the actual surveying and studying of the lands; irrigation survey, which considers the conditions of the arid regions and reports on the feasibility of subjecting them to irrigation projects or otherwise redeeming them for purposes of agriculture; and the preparation of maps, which is based largely on the work of the other two departments. As a result of the work already accomplished by the Survey, which includes investigations in practically all parts of the country, maps are i ued which have proven of great value to many industries, especially in mining and engineering. These maps are of unusually large size, i ued in sectional squares, some of them on a scale of four inches to a mile, so accurate that they have even been used as the basis for the settlement of boundary disputes, The work of the actual surveys may be likened to a general and continuous proce of stock taking of the mineral wealth of the nation. As an instance, in 1921, when there was a profound depre ion in the mining industry, the Survey i ued a book, A World Atlas of Economic Geology, in which was summed up a large amount of the data collected during the years of its work, constituting a quantitative study of the distribution of natural wealth among the various nations of the world, of immense value to economists as weil as the mining industry. ‘doctrine’), the science which investigates the past history of the earth and of its inhabitants, and especially the composition, structure, and contents of the rocky crust. History.—In early times the operation of some of the great physical agents of nature attracted attention, and some notice was paid to minerals, rocks, and even fo ils; but the observations were isolated and haphazard, and were mixed up with theories that were often whimsical and absurd. More enlightened views gradually gained ground during the 16th and 17th centuries as a result of better methods of observation and interpretation. During the later decades of the 18th cent. a great impulse was given to earth study by Werner, who presided at the Freiberg School of Mines in Saxony. Werner examined all the rocks he could in his own district, and cla ified them according to their mineralogical character. Owing to his regarding all rocks as being deposited on the bed of a universal ocean originally, and holding that the ocean had since subsided, he gained for himself and his followers the name of Neptunists. On the other hand, Desmarest and taining the volcanic origin of the rocks of 8S. Europe, were known as Vulcanists. In 1795 Hutton published his Theory of the Earth, which specially drew attention to the constant denudation of the earth’s surface by running water and the deposition of débris on the floor of the ocean by this action, In 1797 Play fair published Illustration of Hution’s Theory, while the following year Sir James Hall proved that molten rock or lava gives rise to rocks a uming different aspects, dependent on the rate of cooling and the pre ure to which it is subjected. William Smith, an Eng. surveyor, established stratigraphical geol., and in 1790 he published his Tabular View of British Strata, and a geological map of England in 1815. He cla ified the strata of the Secondary or Mesozoic formations by their fo ils, and Cuvier and Brongniart, two Fr. naturalists, did the same with the Tertiary or Kainozoic formations. Practical.—The term geology is a wide one, embracing as it does not only study of the actual rocks constituting the earth’s crust, but also the evolution of its surface features, the building up and destruction of continents, and the tracing of the changes in the evolution of plants, animals, and human races which have peopled the earth. This latter branch of geol. can only be pursued by a study of the fo ils found embedded in the various rocks and deposits. Since the introduction of life LS a on the earth, each succeeding period in the earth’s history is marked by some peculiar type of animal or vegetable life, and it is by the fo il remains of these characteristic types that geologists are able to determine to what particular period belong the rocks in which they are found. Geol. calls to its aid almost all other branches of science. Astron. teaches us Eat something of the appearance and nature of the other planets; the telescope reveals nebule in various stages of condensation; and the spectroscope shows the exact composition of the heavenly bodies. Physics supplies data relating to the condition of matter and energy, The researches of the chemical laboratory reveal the complicated compositions of many rocks, while bot. and zool. enable fo il remains to be cla ified accurately. Much is, of course, to be learned from the actual arrangement of the rocks themselves, the older rocks usually underlying the newer. Their composition, arrangement, and fo il contents reveal to us the geographical revolutions of past ages, as, for instance, when the remains of an anc. marine bed are found covered by a lacustrine deposit, overlying which again are proofs of another sea, on the floor of which lie volcanic ashes, thus indicating that the original sea, having receded, had its place taken by a lake, only in turn to give way to a return of the sea at some subsequent period, followed by volcanic activity, the whole series being again uplifted to form land, and thus made acce ible to the geologist who reads the riddle of their changes. The main features of the earth’s surface are determined primarily by movements of elevation and depre ion. When a part of the crust is raised above the ocean it is exposed to various agents of denudation, whereby the rocks are disintegrated and the products are carried, partly in solution but largely by mechanical transportation by water and other means, from higher to lower levels, and eventually to the sea. There they are laid down in beds which in course of time accumulate in thick formations, especially where the sea-flow is gradually subsiding. Shells of organisms gradually build up beds of limy or siliceous material. Owing to subsequent crustal movements these beds may be upraised to form land, and by cementation and pre ure the materials are consolidated and form the Sedimentary Rocks, such as conglomerates. sandstones, shales, and limestones. Be The Igneous Rocks owe the origin to the operation of eruptive and volcanic forces, and are formed by the consolidation of molten magmas derived from the hot interior. Some are thrown out at the surface in the form of lava and give rise to obsidians, pitchstone, basalt, etc., or as fragmentary material yielding tuffs and breccias; others cool and solidify below the surface, and are only exposed by subsequent denudation of the overlying rocks which concealed them— granites, gabbros, and dolerites are examples. Crustal movements and the uprise of heated magmas from below bring about marked changes in the rocks of the crust. Strata are fractured, dislocated, tilted, folded, and contorted; sometimes they are displaced for miles in enormous ma es and occasionally inverted. As a result of heat and pre ure rocks: originally sedimentary or igneous are more or le transformed, their old characters being replaced by new ones. Such rocks are termed Metamorphic, and include gnei es, schists, quartzites, slate, and marble. (For a more detailed account of the structure, etc., of other rocks, see separate articles thereon.) | The origin of the earth is an astronomical problem, and takes us back to the time of the nebula, which, it is supposed, condensed down and _ ultimately formed the solar system. Very little is known of the great interior except that it is very hot, and that it is made up of materials much denser than those which compose the outer rocky crust. This rocky crust, with its envelopes of water and air, is the only part acce ible to direct observation.) The divisions are arranged in historical order, from the oldest at the bottom to the youngest at the top. By noting the order of superposition and by means of fo ils it is po ible to correlate the stratified formations in all parts of the world, to fix their relative age and their position in the geological record. ap The oldest rocks are Archaean gnei es and schists, usually concealed under newer deposits, but appearing at the surface in the N.W. Highlands of Scotland, Scand in a via, Canada, and elsewhere. The schists (Moine and Dalradian) of the HK. and 8. Scot. Highlands are also probably Pre-Cam brian. Torrid on Sandstones underlie Cam brian rocks in N.W. Scotland, and at a few localities in Wales and England schists, volcanic rocks, and sediments of this early age are exposed. Vague traces of organic matter in Pre-Cam brian sediments in America are thought to represent the dawn of life (Hozoic). Definite fo ils occur in the Palaeozoic (ancient life)— the lowest, or Cam brian, system containing only the remains of marine invertebrates. These become more abundant in the Or do vic i an, and air-breathing invertebrates apnear in the Svlurian., QTRATIGRAPHICAL TABLE—THH 3 System Sinaia z Kainozoic or Tertiary..... Paleogene. Mesozoic or Secondary.... Permian.. OCarboniferous..... Devonian Sandstone. Paleeozoic or Primary...... Or do vic i an. Cam brian.. Eozoic or Pre-Cam brian 7 or i don i an!Moine and schists Archean while near the top of this system we meet with the earliest fishes. Primitive sharks and double-breathing fishes are dominant in the Old Red Sandstone, and in the succeeding Carboniferous some vertebrates are found to have emerged out of water and evolved into amphibians. Reptilian remains appear in Permian strata