The Map That Changed the World

by Simon Winchester

  Anthracosia: Nonmarine bivalve common in certian horizons in the British Carboniferous Coal Measures, and a useful stratigraphic indicator.

  Arenaceous: Sandy, composed of sand grains.

  Argillaceous: Rocks or sediments that are composed chiefly of clay and clay minerals.

  Arthropod: The largest phylum in the animal kingdom, with species that inhabit all kinds of environment: Typically they have segmented bodies, jointed appendages, and a hard carapace or exoskeleton. Insects and trilobites are classic arthropods.

  Ashlar: A hewn stone, cut into flat slabs, used for facing buildings.

  Asteroceras: A classic Lower Jurassic ammonite, with an attractively ridgedouter shell, common in the Lias of Yorkshire and elsewhere in northern England.

  Batch: Waste pile from a Somerset coal mine

  Bedding plane: The surface that divides one layer in a sediment from another, usually marked by a change in color, composition, or texture.

  Belemnite: The hard, fossilized calcitic guard, usually pencil-shaped, that is often the only preserved part of a squidlike cephalopod.

  Bituminous coal: The most common form of coal, softer and less pure than anthracite.

  Bivalve: An aquatic mollusk, frequently fossilized, that has two calcareous shells that enclose the living parts of the animal.

  Brachiopod: Solitary, bilaterally symmetrical bivalve marine invertebrate.

  Brash: Loose broken rock forming the highest stratum beneath the soil of certain districts. Cornbrash, brashice. Perhaps a corrupt form of the French brèche.

  Carboniferous limestone: Fossil-rich marine limestone laid down in the Carboniferous era, forming much of the characteristic landscape of the western Pennine Hills and northern Somerset.

  Carstone: A brown sandstone with an interstitial cement of limonite.

  Cephalopod: The most complex and highly organized class of mollusks (with a distinct tentacled head), which include the fossil ammonites and the modern squids, octopuses, and pearly nautilus.

  Cirripede: A low class of crustacean, such as a barnacle.

  Chalk: A soft, porous, and fine-grained limestone, characteristically white in color, most memorably found in the cliffs of southern Kent—“the white cliffs of Dover.”

  Chert: A form of quartz, very finely crystalline, that often forms irregular nodules in other sediments.

  Chronostratigraphy: A geological time scale that uses fixed and internationally defined standard reference points.

  Clay: A sediment defined as having particles less than four microns in diameter.

  Clunch Clay: William Smith’s somewhat inelegant—and quickly replaced—name for what is now called the Oxford Clay.

  Coal: A combustible organic sedimentary rock formed of compressed decomposed plant remains.

  Coal measures: A Western European stratigraphic term used for the rocks of the Upper Carboniferous.

  Coelacanth: A type of bony fish thought to have been extinct for fifty million years before the discovery of a living specimen, classified as Latimeria chalumnae, off the South African coast in 1938.

  Coprolite: Fossilized animal droppings.

  Coral Rag: Coarse-grained rubbly limestone—one of the oldest building stones used in Oxford and the surrounding villages. William Smith’s name for the formation now included in the Corallian.

  Cornbrash: William Smith’s formation name, taken from Wiltshire dialect, for a coarse, shelly limestone of the Great Oolite that disintegrates and breaks up easily, providing soils ideal for growing corn. See also brash.

  Crinoid: A class of echinoid comprising the stalked sea lilies and feather stars.

  Crust: The outermost solid layer of the earth, separated from the underlying mantle by the so-called Mohorovicic Discontinuity.

  Cycad: One of the more important fossil floras of the Mesozoic, resembling small palm trees.

  Cyclothem: A recurring sequence of beds found in many sedimentary rocks, notably in the Upper Carboniferous, in coal-rich series.

  Dip: The angle in degrees between the horizontal and any inclined geological feature, most usually the bedding plane of a series of sediments.

  Dislocations: Any surface across which there is a loss of continuity—for example, a sediment interrupted by a fault.

  Drift: Superficial geological material in a landscape, often brought by ice or glacial meltwater. The term is used in geological mapping, and is distinguished from solid.

  Echinoid: The class of echinoid to which sea urchins and sand dollars belong.

  Estwing: Noted American manufacturer, based in Rockford, Illinois, of geological and other hammers.

  Facies: The combined lithological and paleontological characteristics of a sediment from which it is usually possible to infer the environmental conditions at the time of deposition.

  Fault: A fracture in a geological structure, caused by movement and shear across a surface, resulting in displacement.

  Flint: A microcrystalline form of silica found usually in chalk, which in other sediments is called chert.

  Fool’s gold: Iron pyrite, usually in cubic crystals that have the appearance of yellow metal.

  Forest Marble: An argillaceous laminated shelly limestone in the Great Oolite Series, which when polished passes as marble. Named by William Smith after the Forest of Wychwood, which in his time extended over a much greater area.

  Fossil: Originally an adjective meaning “ancient” now a noun used to denote the preserved remains or evidence, usually found in rocks, of previous organic life.

  Friable: Property of a rock that can be disintegrated by the slightest pressure, such as that between two fingers.

  Freestone: A fine-grained rock that can be cut and sawn with little risk of fracturing.

  Fuller’s Earth: Term used either for the montmorillonite clay employed in the wool industry to remove lanolin or in stratigraphy to define an upper part of the Middle Jurassic in southern England.

  Gastropod: A mollusk with a single coiled shell and a foot, the anterior part of which is developed into a head.

  Genus: A taxonomic term, low in rank (between Family and Species), and usually consisting of closely related species.

  Geology: The study of the solid part of a planet.

  Geotherm: The variation of a temperature with depth in the earth.

  Gondwana: Former southern supercontinent.

  Goniometer: An instrument for measuring the angles between the faces of crystals.

  Graptolite: A tubelike creature, with branched extensions, found in many shales and slates of Ordovician and Silurian age.

  Gymnosperm: Plants—frequently found fossilized in Carboniferous rocks—with their seeds held in cones, as with cycads and ferns.

  Hercynian: A term still occasionally in use for a Permo-Triassic orogenic episode; generally called the Variscan.

  Horsetail: A type of fern commonly found in Carboniferous rocks.

  Ichthyosaur: A fishlike marine reptile, becoming extinct in the Middle Cretaceous.

  Igneous: One of three primary rock types found in Earth’s crust (see also metamorphic, sedimentary), igneous rocks have solidified from molten magma generated deep within the planet.

  Iron pyrite: A metallic-looking sulfide of iron, known jocularly as fool’s gold.

  Kellaway’s Beds: Richly fossiliferous calcareous clay and sandstone beds forming the basement of the Oxford Clay, and resting directly on the cornbrash. Smith’s term for it was “Kelloway’s Stone.”

  Laurasia: Former northern supercontinent.

  Lepidodendron: A tree, commonly found fossilized in Carboniferous coal deposits, notable for its size—up to one hundred feet tall—and scaly bark.

  Lias: Somerset quarryman’s term, from either the pronunciation of the word “layers” or the French for a kind of limestone, which now applies to a period of the Lower Jurassic.

  Lignite: Low-grade brown-black coal.

  Limestone: A sedimentary rock of which the principal ingredient, from either shelly r
emains or precipitates, is calcium carbonate.

  Limonite: A yellow-brown inferior iron ore, often found in large earthy masses in a variety of forms.

  Lingula: A type of brachiopod, still extant, but known from as far back as the Cambrian.

  Lithology: A description of the major macroscopic features of a type of rock—particularly texture, color, and composition.

  Magma: A molten fluid of complex silicates and metals formed within the crust or upper mantle of the earth, which may be extruded by volcanic eruptions or other igneous activity to form solid and consolidated rocks.

  Magnesian limestone: A limestone in which some ten percent of the calcium carbonate has been replaced by a magnesium carbonate, resulting in a much denser and harder lithology.

  Mantle: The zone in the earth between the hard crust and the liquid metallic core.

  Marlstone: A half-formed argillaceous limestone, with a large proportion of clay, microfossils, and relic ooze.

  Metamorphic: One of the three basic rock types (see also sedimentary and igneous) in which pressure, temperature, and time have greatly deformed and recrystallized the original.

  Millstone Grit: A coarse sandstone, found in the Carboniferous of Britain, much used for building in the English North.

  Mollusk: A phylum of animals with a fleshy body usually surrounded by a calcareous shell or shells.

  Montmorillonite: See also smectite. A sheet silicate mineral, found in some clays (most notably fuller’s earth) and widely used for its absorptive powers.

  Mosaic theory: Used to describe the general belief among early geologists in divine creation of the earth, and in the occurrence of the Noachian flood, or Deluge.

  Neptunism: A theory, popularized by Werner, which held that all rocks were precipitates from a primordial ocean.

  Noachian: Pertaining to Noah, and to the persistent belief among nineteenth century geologists that the Flood with which he was associated had profound and global geological significance.

  Oolite: A common limestone composed primarily of tiny spherical accretions of calcium carbonate around a quartz core.

  Orogeny: A period of crustal compression that results in mountain-building and consequent major changes in geological conditions.

  Ostrea: The oyster.

  Outcrop: That part of a rock unit that is exposed at the earth’s surface.

  Overburden: Any loose material that overlies bedrock.

  Paleogeography: The reconstruction, inferred from geological evidence, of the former physical geography of the earth.

  Paleontology: The study of fossil flora and fauna, in the attempt to infer both the age and relative age of the sediments in which the fossils appear, and gauge the nature of the contemporaneous environment.

  Pangea: A supercontinent that existed (according to most theories) for some forty million years from the late Permian to the Triassic. It was, according to these same theorists, surrounded by a superocean, the Panthalassa.

  Pantograph: A jointed parallelogram of slender rods, used by surveyors for copying diagrams and plans on the same (or on a different scale).

  Peat: A thick organic soil deposit that, if dried, is flammable, burning with a characteristic sweet smell. In some senses regarded as a very primitive form of lignite, itself a low-grade coal.

  Petrifaction: One process of making a fossil, in which chemical precipitates are deposited within the porous structure of the shell or other hard parts of an organism.

  Phyllosilicate: A group of silicates with crystal structures arranged in large sheets, common in many argillaceous and low-grade metamorphic rocks.

  Phylum: The second highest taxonomic classification, one of the main divisions of animal and plant kingdoms.

  Plane table: A surveyor’s instrument, used in conjunction with a sighting glass, for marking the relative positions of observed structures and the angles between them.

  Plesiosaur: A large aquatic reptile, in appearance like (as William Buckland put it) “a snake strung through a turtle,” common in the Jurassic.

  Plutonism: The theory, advanced by Hutton, that held that almost all rocks originated as a result of heat and melting, rose from the mantle to form new land, only to decay and be regenerated.

  Portland Stone: An Upper Jurassic mollusk-rich limestone, commonly used for building the grander structures and monument in the large British cities.

  Pterodactyl: A fossil reptile found in Jurassic and Cretaceous sediments, noted for its large jaw and membrane attached to the long fourth digit of its forelimb, enabling it to fly.

  Quarry sap: The trace liquids found in some freestones, which, on freezing, allow the rock to be split along its bedding planes.

  Radiometry: A common means of determining the age of rocks by measuring the relative amounts of “parent” and “daughter” isotopes caused in radioactive decay, the most common pairings being potassiumargon, rubidium-strontium, and samarium-neodymium

  Red Marl: Smith’s name for the Keuper Marl, which consists of red fine-grained siltstones forming the upper part of the Trias.

  Rock: A consolidated or unconsolidated aggregation of mineral or organic matter, formed either by the accretion (sedimentary rocks) of grains or sediments, by the crystallization (igneous rocks) of molten material, or by the alteration (metamorphic rocks) of existing rocks under pressure and heat.

  Sandstone: A sedimentary rock composed of sand-size particles of silicates bound together by a cement that may be carbonate

  Seat earth: A fossil soil, often with plant rootlets still in place, often found immediately beneath a layer of coal.

  Sediment: Solid material—organic and inorganic—that has settled from suspension in a liquid, usually water.

  Sedimentary: Consolidated sediments, usually with organized into strata or with bedding characteristics.

  Seismic: Concerned with the vibration of the earth, whether naturally or artificially induced. Pertaining to earthquakes and crustal movement.

  Shale: An argillaceous rock, noted for its thin and well-defined laminations.

  Siltstone: A consolidated silt, or a clay like rock with particles measuring larger than four microns.

  Slate: A low-grade metamorphic rock, usually argillaceous, and that, because of the extremes of pressure and temperature to which it has been subjected, has well-defined cleavage and bedding planes.

  Smectite: The montmorillonite group of clay minerals, useful for leaching oil from wool.

  Solid: Term used in geological cartography to describe the bedrock, and opposed to the superficial and often glacially derived material, known as drift.

  Stratification: The layered or bedded arrangement of rocks, usually but not uniquely found in sedimentary deposits. There can be stratified lava flows and metamorphic rocks.

  Stratum (pl. strata): A defined layer of sedimentary rock, usually separated from other beds above and below by bedding planes.

  Striations: Small marks and lines, frequently parallel, etched into a solid surface by some external—often glacial—force.

  Strike: The direction taken by a structural surface—most usually a bedding plane, and also a fault—as it intersects the horizontal. Strike is at ninety degrees to the direction of dip.

  Stromatolite: A cumbersome fossiliferous mass of an evidently funguslike former nature.

  Taxonomy: The classification of plants of animals. The main taxa, in descending order, are kingdom, phylum, class, order, family, genus, and species.

  Tectonic: Used in reference to the formation of a major earth structure, usually involving deformation or collision.

  Terebratulid: Order of small brachiopods first appearing in the Devonian, common in the Jurassic, and known in English rural areas as lamp shells.

  Tertiary: One of the great and more recent divisions of the geological time scale, which includes the Eocene, Oligocene, Miocene and Pliocene; hence Tertiaries, rocks laid down or created—like Tertiary basalts—during this period.

  Tethys: The former ocean tha
t broadly separated the two great Mesozoic supercontinental landmasses of Gondwana and Laurasia.

  Theodolite: A surveyor’s instrument for measuring vertical and horizontal angles.

  Titanites: A very large and classical ammonite.

  Trilobite: A common arthropod, with nearly 4000 species, found from the Cambrian to the Permian. Its biography, notable for its importance in displaying Darwinian evolutionary principles, was written by R. Fortey.

  Unconformity: Surface of contact between two series of rocks that is sufficiently unconformable to imply a passage of time and often the occurrence of earth movement between the two periods of deposition.

  Uniformitarianism: James Hutton’s belief, formulated in the late eighteenth century, that the natural occurrences observable today have been occurring for millions of years past, and thus—as in “the present is the key to the past”—indicate the basic processes of geology.

  Variscan: A major orogeny, occurring during the Carboniferous and Permian, relating to the closure of the gap between Africa and Europe. It resulted in the building of many central European mountain chains. See also Hercynian.

  Vein: A deposit of a mineral, usually crystalline, limited to a fissure or joint of a rock; to be compared with a lode, which involves a much wider dissemination of a mineral through a rock body.

  Wernerian: The principles outlined by Abraham Werner of Freiburg, Germany, in the early nineteenth century, which were broadly based on Neptunism, and inspired a large school of mapmakers and students of geology—which Werner himself preferred to term “geognosy.”

  Wollastonite: A silicate mineral noted for its long fibers, used in the making of the insulating material known as rock wool; it was named after William Wollaston, the medal in whose name remains the highest honor that can be given a geologist. The first winner, in 1831, was William Smith.

  Sources and Recommended Reading

  The papers, diaries, sketches, execrable poems, and extraordinary maps of William Smith are kept in the archive of the University Museum, Oxford, as are the papers of his nephew and future Oxford professor of geology, John Phillips, and those of the flamboyantly eccentric omnivore Dean William Buckland. The collections of George Bellas Greenough are in the archives of the Geological Society of London. There are other important papers housed in the Eyles Collection at the University of Bristol.