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  1. ground waterThe water that lies beneath the ground surface, filling the cracks, crevices, and pore space of rocks.

          

  2. lateriteHighly leached soil that forms in regions of tropical climate with high temperatures and very abundant rainfall.

          

  3. stalagmiteCone-shaped mass of dripstone formed on cave floors, generally directly below a stalactite.

          

  4. wave-cut platformA plane containing all of the hinge lines of a fold.

          

  5. oil fieldAn area underlain by one or more oil pools.

          

  6. gaining streamA stream that receives water from the zone of saturation.

          

  7. O horizonThe physical removal of rock by an agent such as running water, glacial ice, or wind.

          

  8. graded bedA stream that exhibits a delicate balance between its transporting capacity and the sediment load available to it.

          

  9. joint setJoints oriented in one direction approximately parallel to one another.

          

  10. hematiteA type of iron oxide that has a brick-red color when powdered; Fe2O3.

          

  11. barrier islandHeavy or large sediment particles in a stream that travel near or on the stream bed.

          

  12. glacierSediment composed of particles with diameter less than 1/256 mm.

          

  13. chemical sedimentary rockA rock composed of material precipitated directly from solution.

          

  14. original horizontalityThe deposition of most water-laid sediment in horizontal or near-horizontal layers that are essentially parallel to Earth's surface.

          

  15. intermediateHighly leached soil that forms in regions of tropical climate with high temperatures and very abundant rainfall.

          

  16. frost wedgingA type of frost action in which the expansion of freezing water pries a rock apart.

          

  17. polar wanderingSeismic wave that travels through Earth's interior.

          

  18. foldBend in layered bedrock.

          

  19. lava flowsSlow-to-rapid mass wasting in which debris moves downslope as a very viscous fluid.

          

  20. calderaA volcanic depression much larger than the original crater.

          

  21. crystal settlingThe process whereby the minerals that crystallize at a high temperature in a cooling magma move downward in the magma chamber because they are denser than the magma.

          

  22. springA place where water flows naturally out of rock onto the land surface.

          

  23. hinge lineLine about which a fold appears to be hinged. Line of maximum curvature of a folded surface.

          

  24. fringing reefA reef separated from the shoreline by the deeper water of a lagoon.

          

  25. schistThe solid material that precipitates in the pore space of sediments, binding the grains together to form solid rock.

          

  26. lateral continuityMovement in which the entire glacier slides along as a single body on its base over the underlying rock.

          

  27. soil horizonAny of the layers of soil that are distinguishable by characteristic physical or chemical properties.

          

  28. angular unconformityThe deposition of most water-laid sediment in horizontal or near-horizontal layers that are essentially parallel to Earth's surface.

          

  29. environment of depositionMechanical weathering of rock by freezing water.

          

  30. mountain rangeA group of closely spaced mountains or parallel ridges.

          

  31. compressive stressA narrow, deep trough parallel to the edge of a continent or an island arc.

          

  32. shear forcePartly hollow, globelike body found in limestone or other cavernous rock.

          

  33. axial planeIn an intrusion, the finer-grained rock adjacent to a contact with country rock.

          

  34. bondingBend in layered bedrock.

          

  35. isostatic adjustmentDetermining the age of a rock or mineral through its radioactive elements and decay products (previously and somewhat inaccurately called radiometric or radioactive dating).

          

  36. AsthenosphereThe oldest eon of Earth's history.

          

  37. overturned foldA fold overturned to such an extent that the limbs are essentially horizontal.

          

  38. volcanismA sedimentary rock composed mostly of the mineral dolomite.

          

  39. Curie pointThe temperature below which a material becomes magnetized.

          

  40. cross-beddingAn arrangement of relatively thin layers of rock inclined at an angle to the more nearly horizontal bedding planes of the larger rock unit.

          

  41. geologic cross sectionChange in direction of waves due to slowing as they enter shallow water. (End Chapter 14)

          

  42. hanging valleyA smaller valley that terminates abruptly high above a main valley.

          

  43. oil poolUnderground accumulation of oil.

          

  44. modified Mercalli scaleScale expressing intensities of earthquakes (judged on amount of damage done) in Roman numerals ranging from I to XII.

          

  45. beach faceA theoretical downward limit for stream erosion of Earth's surface.

          

  46. guyotFlat-topped seamount.

          

  47. Amphibole groupThe sum of the weight of the subatomic particles in an average atom of an element, given in atomic mass units.

          

  48. atomic mass numberA pronounced sinuous curve along a stream's course.

          

  49. earthquakeA mound of loose sand grains heaped up by the wind.

          

  50. crystal formArrangement of various faces on a crystal in a definite geometric relationship to one another.

          

  51. AndesiteFine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesian minerals. (Begin Chapter 3)

          

  52. AftershockMaterial deposited by debris-laden meltwater from a glacier.

          

  53. terrigenous sedimentand interrelationships of rock units.

          

  54. debris fallA free-falling mass of debris.

          

  55. marine terraceThe total amount of space taken up by openings between sediment grains.

          

  56. permafrostGround that remains permanently frozen for many years.

          

  57. pyroclastAny of the large crystals in porphyritic igneous rock.

          

  58. framework silicate structureCrystal structure in which all four oxygen ions of a silica tetrahedron are shared by adjacent ions.

          

  59. circum-Pacific beltMajor belt around the edge of the Pacific Ocean on which most composite volcanoes are located and where many earthquakes occur.

          

  60. Phanerozoic EonA line of batholiths or volcanoes. Generally the line, as seen from above, is curved.

          

  61. elastic rebound theoryStream that loses water to the zone of saturation.

          

  62. wavelengthThe horizontal distance between two wave crests (or two troughs).

          

  63. petroleumCrude oil and natural gas. (Some geologists use petroleum as a synonym for oil.)

          

  64. glassy (vitreous) lusterA luster that gives a substance a glazed, porcelainlike appearance.

          

  65. turbidity currentThe temperature below which a material becomes magnetized.

          

  66. passive continental marginLarge fan-shaped pile of sediment that usually forms where a stream's velocity decreases as it emerges from a narrow canyon onto a flat plain at the foot of a mountain range.

          

  67. loamSoil containing approximately equal amounts of sand, silt, and clay.

          

  68. depth of focusThe physical removal of rock by an agent such as running water, glacial ice, or wind.

          

  69. intrusion (intrusive structure)A body of intrusive rock classified on the basis of size, shape, and relationship to surrounding rocks.

          

  70. Recent (Holocene) EpochThe present epoch of the Quaternary Period.

          

  71. metallic lusterThe most recent of the eras; followed the Mesozoic Era.

          

  72. chemical weatheringThe decomposition of rock resulting from exposure to water and atmospheric gases.

          

  73. transform plate boundaryThe portion of a fracture zone between two offset segments of a mid oceanic ridge crest.

          

  74. craterThe quality and intensity of light reflected from the surface of a mineral.

          

  75. barrier reefA reef separated from the shoreline by the deeper water of a lagoon.

          

  76. silicic (felsic)A substance that contains silica as part of its chemical formula.

          

  77. natural leveeLow ridges of flood-deposited sediment formed on either side of a stream channel, which thin away from the channel.

          

  78. pillow structure (pillow basalts)Rocks, generally basalt, formed in pillow shaped masses fitting closely together; caused by underwater lava flows.

          

  79. lavaMajor subdivision of the standard geologic time scale (e.g., Mesozoic Era).

          

  80. abyssal fanArrangement of various faces on a crystal in a definite geometric relationship to one another.

          

  81. debrisAn explanation for observed phenomena that has a high possibility of being true.

          

  82. extrusive rockThe physical removal of rock by an agent such as running water, glacial ice, or wind.

          

  83. seismic waveA wave of energy produced by an earthquake.

          

  84. cleavageThe ability of a mineral to break along preferred planes.

          

  85. frost heavingA theoretical downward limit for stream erosion of Earth's surface.

          

  86. mantle plumeA mound of loose sand grains heaped up by the wind.

          

  87. slatyIn mass wasting, movement of a relatively coherent descending mass along one or more well-defined surfaces.

          

  88. clay mineral groupCollective term for several clay minerals.

          

  89. cinder coneDistinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of about 30° to 60°.

          

  90. magnitudeA fracture in bedrock along which movement has taken place.

          

  91. Prearchean (Hadean) EonThe earliest Eon of Earth's history.

          

  92. downcuttingThe sliding of the sea floor beneath a continent or island arc.

          

  93. hornA sharp peak formed where cirques cut back into a mountain on several sides.

          

  94. limoniteIron/magnesium bearing mica.

          

  95. flank eruptionAn eruption in which lava erupts out of a vent on the side of a volcano.

          

  96. mechanical weatheringThe physical disintegration of rock into smaller pieces.

          

  97. direction of dipElongate region in which subduction takes place.

          

  98. ductileIron/magnesium bearing mica.

          

  99. breakerA long, sinuous ridge of sediment deposited by glacial meltwater.

          

  100. lusterA fine-grained sedimentary rock (grains finer than 1/16 mm in diameter) formed by the cementation of silt and clay (mud). Shale has thin layers (laminations) and an ability to split (fissility) into small chips.

          

  101. faultA fracture in bedrock along which movement has taken place.

          

  102. crustVery slow, continuous downslope movement of soil or debris. (Begin Chapter 9)

          

  103. Archean EonThe oldest eon of Earth's history.

          

  104. rotational slide (slump)Large, symmetrical ridge of sand parallel to the wind direction.

          

  105. dip-slip faultA fault in which movement is parallel to the dip of the fault surface.

          

  106. body waveNaturally occurring material that can be profitably mined.

          

  107. Cenozoic EraA set of conditions that hold petroleum in a reservoir rock and prevent its escape by migration.

          

  108. sheetwashWater flowing down a slope in a layer.

          

  109. lateral erosionErosion and undercutting of stream banks caused by a stream swinging from side to side across its valley floor.

          

  110. geothermal gradientThe upper surface of the zone of saturation.

          

  111. scientific methodA means of gaining knowledge through objective procedures.

          

  112. mudflowA flowing mixture of debris and water, usually moving down a channel.

          

  113. fossilTraces of plants or animals preserved in rock.

          

  114. eonPartly hollow, globelike body found in limestone or other cavernous rock.

          

  115. right-lateral faultBroad, flat-topped area elevated above the surrounding land and bounded, at least in part, by cliffs.

          

  116. U-shaped valleyThe overlying surface of an inclined fault plane.

          

  117. permeabilityThe capacity of a rock to transmit a fluid such as water or petroleum.

          

  118. AbrasionThe grinding away of rock by friction and impact during transportation. (Begin Chapter 10)

          

  119. transverse duneA rock containing organic matter that is converted to petroleum by burial and other postdepositional changes.

          

  120. index fossilA theoretical downward limit for stream erosion of Earth's surface.

          

  121. half-lifeA fold in which the layered rock usually dips toward an axis.

          

  122. sillA term used for oxygen plus silicon.

          

  123. convectionA very slow circulation of a substance driven by differences in temperature and density within that substance.

          

  124. stressA force acting on a body, or rock unit, that tends to change the size or shape of that body, or rock unit. Force per unit area within a body.

          

  125. isotopeIron/magnesium bearing mica.

          

  126. plunging foldA fold in which the hinge line (or axis) is not horizontal.

          

  127. hydrologic cycleThe movement of water and water vapor from the sea to the atmosphere, to the land, and back to the sea and atmosphere again.

          

  128. sheet jointsCracks that develop parallel to the outer surface of a large mass of expanding rock, as pressure is released during unloading.

          

  129. fallA tabular intrusive structure concordant with the country rock.

          

  130. viscosityResistance to flow.

          

  131. seismogramRock that forms from crystals precipitating during evaporation of water.

          

  132. blockLarge angular pyroclast.

          

  133. mineralMajor subdivision of the standard geologic time scale (e.g., Mesozoic Era).

          

  134. epochStrip of sediment, usually sand but sometimes pebbles, boulders, or mud, that extends from the low-water line inland to a cliff or zone of permanent vegetation.

          

  135. geologic resourcesValuable materials of geologic origin that can be extracted from Earth.

          

  136. solifluctionAny of the layers of soil that are distinguishable by characteristic physical or chemical properties.

          

  137. arrangementThe grinding away of rock by friction and impact during transportation. (Begin Chapter 10)

          

  138. anticlineAn arched fold in which the rock layers usually dip away from the axis of the fold.

          

  139. plateauPortion of a continent that has been structurally stable for a prolonged period of time.

          

  140. basal slidingMovement in which the entire glacier slides along as a single body on its base over the underlying rock.

          

  141. phenocrystThe outer layer of rock, forming a thin skin over Earth's surface.

          

  142. abyssal plainDescribing a substance in which the atoms are arranged in a regular, repeating, orderly pattern.

          

  143. Mediterranean beltThe upper surface of the zone of saturation.

          

  144. transported soilSoil not formed from the local rock but from parent material brought in from some other region and deposited, usually by running water, wind, or glacial ice.

          

  145. structural basinChange in size (volume) or shape of a body (or rock unit) in response to stress.

          

  146. magnetic poleAn area where the strength of the magnetic field is greatest and where the magnetic lines of force appear to leave or enter Earth.

          

  147. earthflowA type of movement that implies that a descending mass is moving downslope as a viscous fluid.

          

  148. left-lateral faultA strike-slip fault in which the block seen across the fault appears displaced to the left.

          

  149. divergent boundaryThe capacity of a rock to transmit a fluid such as water or petroleum.

          

  150. textureThe central zone of Earth.

          

  151. source rockA rock containing organic matter that is converted to petroleum by burial and other postdepositional changes.

          

  152. stalactiteIciclelike pendant of dripstone formed on cave ceilings.

          

  153. silicatesA substance that contains silica as part of its chemical formula.

          

  154. losing streamA stream that receives water from the zone of saturation.

          

  155. spheroidal weatheringRounded by weathering from an initial blocky shape.

          

  156. geodeA fine-grained rock that splits easily along flat, parallel planes.

          

  157. plate tectonicsA theory that Earth's surface is divided into a few large, thick plates that are slowly moving and changing in size. Intense geologic activity occurs at the plate boundaries.

          

  158. focusEach period of the standard geologic time scale is divided into epochs (e.g., Pleistocene Epoch of the Quaternary Period).

          

  159. stream terraceSteplike landform found above a stream and its flood plain.

          

  160. chill zoneDistinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of about 30° to 60°.

          

  161. faunal successionA principle or law stating that fossil species succeed one another in a definite and recognizable order; in general, fossils in progressively older rock show increasingly greater differences from species living at present.

          

  162. hydrothermal rockA rock containing organic matter that is converted to petroleum by burial and other postdepositional changes.

          

  163. active continental marginA margin consisting of a continental shelf, a continental slope, and an oceanic trench.

          

  164. clastic textureNarrow column of hot mantle rock that rises and spreads radially outward.

          

  165. shearingMovement in which parts of a body slide relative to one another and parallel to the forces being exerted.

          

  166. alluvial fanA plane containing all of the hinge lines of a fold.

          

  167. gravity meterAn instrument that measures the gravitational attraction between Earth and a mass within the instrument.

          

  168. surface waveRapid sliding of a mass of bedrock along an inclined surface of weakness.

          

  169. coastal straighteningThe gradual straightening of an irregular shoreline by wave erosion of headlands and wave deposition in bays.

          

  170. hanging wallA type of surface seismic wave that behaves like a rolling ocean wave and causes the ground to move in an elliptical path.

          

  171. mica groupGroup of minerals with a sheet silicate structure.

          

  172. oil sandAsphalt-cemented sand deposit.

          

  173. composite volcano (stratovolcano)The gradual straightening of an irregular shoreline by wave erosion of headlands and wave deposition in bays.

          

  174. accumulation stageStage in the evolution of major mountain belts characterized by the accumulation of great thicknesses (several kilometers) of sedimentary or volcanic rocks.

          

  175. lithospheric delamination (or delamination)The detachment of part of the mantle portion of the lithosphere beneath a mountain belt.

          

  176. tensional stressStress due to forces that tend to cause movement or strain parallel to the direction of the forces.

          

  177. nonconformityAn unconformity in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock.

          

  178. atomic numberThe total number of protons in an atom.

          

  179. natural gasA gaseous mixture of naturally occurring hydrocarbons.

          

  180. contact metamorphismMetamorphism under conditions in which high temperature is the dominant factor.

          

  181. hardnessThe relative ease or difficulty with which a smooth surface of a mineral can be scratched; commonly measured by Mohs' scale.

          

  182. organic sedimentary rockRock composed mostly of the remains of plants and animals.

          

  183. rockNaturally formed, consolidated material composed of grains of one or more minerals. (There are a few exceptions to this definition.

          

  184. clastic sedimentary rockA sedimentary rock composed of fragments of preexisting rock.

          

  185. continental slopeA relatively steep slope extending from a depth of 100 to 200 meters at the edge of the continental shelf down to oceanic depths.

          

  186. meanderA pronounced sinuous curve along a stream's course.

          

  187. dataObservations or measurements used by scientists to test hypotheses.

          

  188. seismic sea waveSee tsunami.

          

  189. debris flowSlow-to-rapid mass wasting in which debris moves downslope as a very viscous fluid.

          

  190. chertThe land near the sea, including the beach and a strip of land inland from the beach.

          

  191. cone of depressionA vertical angle measured downward from the horizontal plane to an inclined plane. (Begin Chapter 15)

          

  192. strike-slip faultA fault in which movement is parallel to the strike of the fault surface.

          

  193. rhyoliteA fine-grained, felsic, igneous rock made up mostly of feldspar and quartz.

          

  194. oil trapAsphalt-cemented sand deposit.

          

  195. migmatiteMixed igneous and metamorphic rock.

          

  196. compressive stressA narrow, deep trough parallel to the edge of a continent or an island arc.

          

  197. maficSilica-deficient igneous rock with a relatively high content of magnesium, iron, and calcium.

          

  198. creepA moving body of water, confined in a channel and running downhill under the influence of gravity.

          

  199. protonA subatomic particle that contributes mass and a single positive electrical charge to an atom.

          

  200. karst topographyA region of Earth's outer shell beneath the lithosphere. The asthenosphere is of indeterminate thickness and behaves plastically. (Begin Chapter 1)

          

  201. atomA small rock island that is an erosional remnant of a headland left behind as a wave-eroded coast retreats inland.

          

  202. earthy lusterA fine-grained, felsic, igneous rock made up mostly of feldspar and quartz.

          

  203. bed loadHeavy or large sediment particles in a stream that travel near or on the stream bed.

          

  204. Mohs'hardness scale Scale on which ten minerals are designated as standards of hardness.

          

  205. fault-block mountain rangeA range created by uplift along normal or vertical faults.

          

  206. slateA fine-grained rock that splits easily along flat, parallel planes.

          

  207. divergent plate boundaryBoundary separating two plates moving away from each other.

          

  208. intrusive rockA rock that is sufficiently porous and permeable to store and transmit petroleum.

          

  209. depositionThe removal of clay, silt, and sand particles from the land surface by wind.

          

  210. oceanic trenchA narrow, deep trough parallel to the edge of a continent or an island arc.

          

  211. unconformityA surface that represents a break in the geologic record, with the rock unit immediately above it being considerably younger than the rock beneath.

          

  212. positive gravity anomalyA margin that includes a continental shelf, continental slope, and continental rise that generally extends down to an abyssal plain at a depth of about 5 kilometers.

          

  213. tuffA rock formed from fine-grained pyroclastic particles (ash and dust).

          

  214. fractureCapable of being molded and bent under stress.

          

  215. porosityThe percentage of a rock's volume that is taken up by openings.

          

  216. plutonMolten rock, usually mostly silica. The liquid may contain dissolved gases as well as some solid minerals.

          

  217. mafic rockSilica-deficient igneous rock with a relatively high content of magnesium, iron, and calcium.

          

  218. heavy crudeDense, viscous petroleum that flows slowly or not at all.

          

  219. superpositionThe sliding of the sea floor beneath a continent or island arc.

          

  220. ductile (plastic)A luster giving a substance the appearance of unglazed pottery.

          

  221. arêteMajor subdivision of the standard geologic time scale (e.g., Mesozoic Era).

          

  222. tectonic forcesIn mass wasting, the component of gravitational force that is parallel to an inclined surface.

          

  223. normal faultA fault in which the hanging-wall block moved down relative to the footwall block.

          

  224. rain shadowA region on the downwind side of mountains that has little or no rain because of the loss of moisture on the upwind side of the mountains.

          

  225. speleothemA line along which the temperature of rock (or other material) is the same.

          

  226. periodA place where water flows naturally out of rock onto the land surface.

          

  227. Love waveThe opening in Earth's surface through which a volcanic eruption takes place.

          

  228. formationA body of rock of considerable thickness that has a recognizable unity or similarity making it distinguishable from adjacent rock units. Usually composed of one bed or several beds of sedimentary rock, although the term is also applied to units of metamorphic and igneous rock. A convenient unit for mapping, describing, or interpreting the geology of a region.

          

  229. magnetic fieldRegion of magnetic force that surrounds Earth.

          

  230. superposed streamA stream that receives water from the zone of saturation.

          

  231. synclineA fold in which the layered rock usually dips toward an axis.

          

  232. eskerA long, sinuous ridge of sediment deposited by glacial meltwater.

          

  233. conglomerateShale with a high content of organic matter from which oil may be extracted by distillation.

          

  234. AsthenosphereAn explanation for observed phenomena that has a high possibility of being true.

          

  235. terrane (tectonostratigraphic terrane)A region in which the geology is markedly different from that in adjoining regions.

          

  236. isothermA line along which the temperature of rock (or other material) is the same.

          

  237. plutonic rockA single, negative electric charge that contributes virtually no mass to an atom.

          

  238. silicaA term used for oxygen plus silicon.

          

  239. dissolved loadThe portion of the total sediment load in a stream that is carried in solution.

          

  240. volcanic domeA large, rounded landform developed in a massive rock, such as granite, by the process of exfoliation.

          

  241. receding glacierA drainage pattern in which streams diverge outward like spokes of a wheel.

          

  242. divideA tabular intrusive structure concordant with the country rock. (End Chapter 6)

          

  243. differentiationThe movement of eroded particles by agents such as rivers, waves, glaciers, or wind.

          

  244. elementA type of iron oxide that is yellowish-brown when powdered; Fe2O3•nH2O.

          

  245. estuaryDrowned river mouth.

          

  246. shear strengthMovement in which parts of a body slide relative to one another and parallel to the forces being exerted.

          

  247. Bowen's reaction seriesThe gradual straightening of an irregular shoreline by wave erosion of headlands and wave deposition in bays.

          

  248. differential weatheringVarying rates of weathering resulting from some rocks in an area being more resistant to weathering than others.

          

  249. dendritic patternDrainage pattern of a river and its tributaries, which resembles the branches of a tree or veins in a leaf.

          

  250. end moraineChange in size (volume) or shape of a body (or rock unit) in response to stress.

          

  251. exfoliationThe stripping of concentric rock slabs from the outer surface of a rock mass.

          

  252. slip faceA ferromagnesian mineral with the formula (Fe, Mg)2SiO4.

          

  253. zone of accumulationThat portion of a glacier in which ice is lost.

          

  254. cross-cutting relationshipA principle or law stating that a disrupted pattern is older than the cause of disruption.

          

  255. neutronA fracture in bedrock along which movement has taken place.

          

  256. dischargeIn a stream, the volume of water that flows past a given point in a unit of time.

          

  257. pumiceA frothy volcanic glass.

          

  258. foliationParallel alignment of textural and structural features of a rock.

          

  259. orogenyAn episode of intense deformation of the rocks in a region, generally accompanied by metamorphism and plutonic activity.

          

  260. hypothesisIron/magnesium bearing mica.

          

  261. gabbroA mafic, coarse-grained igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.

          

  262. convergent plate boundaryTriangular facet where the lower end of a ridge has been eroded by glacial ice.

          

  263. brittleA fingerlike ridge of sediment attached to land but extending out into open water.

          

  264. metamorphic faciesMetamorphic rocks that contain the same set of pressure or temperature sensitive minerals are regarded as belonging to the same facies, implying that they formed under broadly similar pressure and temperature conditions.

          

  265. ventifactLoose, solid particles that can originate by (1) weathering and erosion of preexisting rocks, (2) chemical precipitation from solution, usually in water, and (3) secretion by organisms.

          

  266. drumlinA fold in which the layered rock usually dips toward an axis.

          

  267. subductionParallel alignment of textural and structural features of a rock.

          

  268. metasomatismMetamorphism coupled with the introduction of ions from an external source.

          

  269. continental glaciationThe covering of a large region of a continent by a sheet of glacial ice.

          

  270. open-pit mineMine in which ore is exposed at the surface in a large excavation.

          

  271. ore mineralThe lower edge of a glacier.

          

  272. slaty cleavageA fold in which the layered rock usually dips toward an axis.

          

  273. quartziteA rock composed of sand-sized grains of quartz that have been welded together during metamorphism.

          

  274. pelagic sedimentA gently sloping erosional surface cut into the solid rock of a mountain range in a dry region; usually covered with a thin veneer of gravel.

          

  275. wave refractionThe bending of seismic waves as they pass from one material to another.

          

  276. coreThe central zone of Earth.

          

  277. heat flowSlow-to-rapid mass wasting in which debris moves downslope as a very viscous fluid.

          

  278. striationsOn minerals, extremely straight, parallel lines. (End Chapter 2)

          

  279. footwallThe underlying surface of an inclined fault plane.

          

  280. distributaryFor igneous rocks, refers to the size of mineral crystals in the rock.

          

  281. negative magnetic anomalyLess than average strength of Earth's magnetic field.

          

  282. placer mineHighly leached soil that forms in regions of tropical climate with high temperatures and very abundant rainfall.

          

  283. PrecambrianMovement in which parts of a body slide relative to one another and parallel to the forces being exerted.

          

  284. beachStrip of sediment, usually sand but sometimes pebbles, boulders, or mud, that extends from the low-water line inland to a cliff or zone of permanent vegetation.

          

  285. drawdownThe grinding away of rock by friction and impact during transportation. (Begin Chapter 10)

          

  286. outwashMaterial deposited by debris-laden meltwater from a glacier.

          

  287. theory of glacial agesAn explanation for observed phenomena that has a high possibility of being true.

          

  288. hydraulic actionThe ability of water to pick up and move rock and sediment.

          

  289. rockfallRock falling freely or bouncing down a cliff.

          

  290. coarse-grained rockRock in which most of the grains are larger than 1 millimeter (igneous) or 2 millimeters (sedimentary).

          

  291. vesicleRounded particles coarser than 2 mm in diameter.

          

  292. headward erosionThe lengthening of a valley in an uphill direction above its original source by gullying, mass wasting, and sheet erosion.

          

  293. crest (of wave)The low point of a wave.

          

  294. soilObservations or measurements used by scientists to test hypotheses.

          

  295. plateBroad, flat-topped area elevated above the surrounding land and bounded, at least in part, by cliffs.

          

  296. continental shelfPressure applied equally on all surfaces of a body; also called geostatic or lithostatic pressure.

          

  297. base levelA theoretical downward limit for stream erosion of Earth's surface.

          

  298. contactsBoulder, cobble, or pebble with flat surfaces caused by the abrasion of wind-blown sand. (End Chapter 13)

          

  299. advancing glacierTotal area drained by a stream and its tributaries.

          

  300. bombLarge spindle- or lens-shaped pyroclast.

          

  301. longshore currentNarrow currents that flow straight out to sea in the surf zone, returning water seaward that has been pushed ashore by breaking waves.

          

  302. confined (artesian) aquiferLarge, symmetrical ridge of sand parallel to the wind direction.

          

  303. equilibriumMaterial is in equilibrium if it is adjusted to the physical and chemical conditions of its environment so that it does not change or alter with time.

          

  304. inclusionA fragment of rock that is distinct from the body of igneous rock in which it is enclosed.

          

  305. stream channelA long, narrow depression, shaped and more or less filled by a stream.

          

  306. trellis patternA drainage pattern consisting of parallel main streams with short tributaries meeting them at right angles. (End Chapter 10)

          

  307. convergent boundaryA boundary between two plates that are moving toward each other.

          

  308. evaporateRock that forms from crystals precipitating during evaporation of water.

          

  309. S waveSediment composed of particles with a diameter between 1/16 mm and 2 mm.

          

  310. rectangular patternA drainage pattern in which tributaries of a river change direction and join one another at right angles.

          

  311. compactionA loss in overall volume and pore space of a rock as the particles are packed closer together by the weight of overlying material.

          

  312. Mediterranean-Himalayan beltA major concentration of earthquakes and composite volcanoes that runs through the Mediterranean Sea, crosses the Mideast and the Himalaya, and passes through the East Indies.

          

  313. water tableThe upper surface of the zone of saturation.

          

  314. blowoutThe physical removal of rock by an agent such as running water, glacial ice, or wind.

          

  315. ventBreaking waves.

          

  316. barSediment composed of particles with diameter less than 1/256 mm.

          

  317. truncated spurTriangular facet where the lower end of a ridge has been eroded by glacial ice.

          

  318. playaMagma on Earth's surface.

          

  319. fjordBend in layered bedrock.

          

  320. graded streamA stream that exhibits a delicate balance between its transporting capacity and the sediment load available to it.

          

  321. ice capA glacier covering a relatively small area of land but not restricted to a valley.

          

  322. rock flourA powder of fine fragments of rock produced by glacial abrasion.

          

  323. Paleozoic EraThe era that followed the Precambrian and began with the appearance of complex life, as indicated by fossils.

          

  324. basaltA fracture in bedrock along which movement has taken place.

          

  325. relative timeThe sequence in which events took place (not measured in time units).

          

  326. spitA fingerlike ridge of sediment attached to land but extending out into open water.

          

  327. radioactive decayA glacier covering a relatively small area of land but not restricted to a valley.

          

  328. volcanic neckA mode of transport that carries sediment downcurrent in a series of short leaps or bounces.

          

  329. rock cycleA type of surface seismic wave that causes the ground to move side to side in a horizontal plane perpendicular to the direction the wave is traveling.

          

  330. rockslideRapid sliding of a mass of bedrock along an inclined surface of weakness.

          

  331. columnar structure (columnar jointing)Rocks, generally basalt, formed in pillow shaped masses fitting closely together; caused by underwater lava flows.

          

  332. plastic flowBroad, flat-topped area elevated above the surrounding land and bounded, at least in part, by cliffs.

          

  333. andesiteLine dividing one drainage basin from another.

          

  334. tarnsSee rock-basin lake.

          

  335. reefA resistant ridge of calcium carbonate formed on the sea floor by corals and coralline algae.

          

  336. isotopic datingDetermining the age of a rock or mineral through its radioactive elements and decay products (previously and somewhat inaccurately called radiometric or radioactive dating).

          

  337. surfBreaking waves.

          

  338. gneissicThe texture of a metamorphic rock in which minerals are separated into light and dark layers or lenses.

          

  339. strip mineA mine in which the valuable material is exposed at the surface by removing a strip of overburden.

          

  340. drainage basinA structure in which the beds dip toward a central point.

          

  341. trough (of wave)A seismic wave propagated by a shearing motion, which causes rock to vibrate perpendicular to the direction of wave propagation.

          

  342. Precambrian shieldThe vast amount of time that preceded the Paleozoic Era.

          

  343. densityWeight per given volume of a substance.

          

  344. diaperLine dividing one drainage basin from another.

          

  345. gneissA broad, flat-topped hill bounded by cliffs and capped with a resistant rock layer.

          

  346. moraineA body of till either being carried on a glacier or left behind after a glacier has receded.

          

  347. saltationA small rock island that is an erosional remnant of a headland left behind as a wave-eroded coast retreats inland.

          

  348. limbA very flat surface underlain by hard, mud-cracked clay.

          

  349. drainage patternThe arrangement in map view of a river and its tributaries.

          

  350. biotiteLine dividing one drainage basin from another.

          

  351. nucleusProtons and neutrons form the nucleus of an atom. Although the nucleus occupies an extremely tiny fraction of the volume of the entire atom, practically all the mass of the atom is concentrated in the nucleus.

          

  352. plateau basaltsLayers of basalt flows that have built up to great thicknesses.

          

  353. atomic weightJoints oriented in one direction approximately parallel to one another.

          

  354. cratonPortion of a continent that has been structurally stable for a prolonged period of time.

          

  355. C horizonA soil layer composed of incompletely weathered parent material.

          

  356. magnetometerAn instrument that measures the strength of Earth's magnetic field.

          

  357. pore spaceThe total amount of space taken up by openings between sediment grains.

          

  358. island arcA curved line of islands.

          

  359. varveA fracture in bedrock along which movement has taken place.

          

  360. veinFracture in rock usually filled with late stage magmatic minerals and often containing metal ore. (End Chapter 7)

          

  361. limestoneA sedimentary rock composed mostly of calcite.

          

  362. solutionA subatomic particle that contributes mass and a single positive electrical charge to an atom.

          

  363. strainA sharp peak formed where cirques cut back into a mountain on several sides.

          

  364. angle of dipA vertical angle measured downward from the horizontal plane to an inclined plane. (Begin Chapter 15)

          

  365. major mountain beltA long chain (thousands of kilometers) of mountain ranges.

          

  366. olivineChange in size (volume) or shape of a body (or rock unit) in response to stress.

          

  367. paleomagnetismiron oxide that is attracted to a magnet.

          

  368. geologic mapA map representing the geology of a given area.

          

  369. claySediment composed of particles with diameter less than 1/256 mm.

          

  370. vadose zoneA subsurface zone in which rock openings are generally unsaturated and filled partly with air and partly with water; above the saturated zone.

          

  371. reservesAny unconsolidated material at Earth's surface.

          

  372. isostasyResistance to flow.

          

  373. rift valleyA tensional valley bounded by normal faults. Rift valleys are found at diverging plate boundaries on continents and along the crest of the mid-oceanic ridge.

          

  374. nonrenewable resourceA resource that forms at extremely slow rates compared to its rate of consumption.

          

  375. xenolith FragmentThe most recent of the eras; followed the Mesozoic Era.

          

  376. elastic limitThe sequence in which events took place (not measured in time units).

          

  377. resourcesThe total amount of a geologic material in all its deposits, discovered and undiscovered (see reserves).

          

  378. point barA stream bar (see definition) deposited on the inside of a curve in the stream, where the water velocity is low.

          

  379. landslideA thick shell of rock that separates Earth's crust above from the core below.

          

  380. deflationA body of sediment deposited at the mouth of a river when the river velocity decreases as it flows into a standing body of water.

          

  381. continental driftA concept suggesting that continents move over Earth's surface.

          

  382. peridotiteAn ultramafic rock composed primarily of the mineral olivine.

          

  383. wellA fingerlike ridge of sediment attached to land but extending out into open water.

          

  384. shadow zoneA subsurface zone in which rock openings are generally unsaturated and filled partly with air and partly with water; above the saturated zone.

          

  385. porphyritic rockAn igneous rock in which large crystals are enclosed in a matrix (or ground mass) of much finer-grained minerals or obsidian.

          

  386. crystallizationCrystal development and growth.

          

  387. BajadaA term used for oxygen plus silicon.

          

  388. hot springMovement in which parts of a body slide relative to one another and parallel to the forces being exerted.

          

  389. tomboloA sedimentary rock formed from the consolidation of plant material. It is rich in carbon, usually black, and burns readily.

          

  390. transform boundaryThe rise of Earth's crust after the removal of glacial ice.

          

  391. meander cutoffA pronounced sinuous curve along a stream's course.

          

  392. crevasseA depression caused by the melting of a stagnant block of ice that was surrounded by sediment.

          

  393. hornfelsA fine-grained, unfoliated metamorphic rock.

          

  394. physical continuityBeing able to physically follow a rock unit between two places.

          

  395. tractionA loss in overall volume and pore space of a rock as the particles are packed closer together by the weight of overlying material.

          

  396. quartzMineral with the formula SiO2.

          

  397. standard geologic time scaleCone-shaped mass of dripstone formed on cave floors, generally directly below a stalactite.

          

  398. slideIn mass wasting, movement of a relatively coherent descending mass along one or more well-defined surfaces.

          

  399. gravitational collapse and spreadingThe earliest Eon of Earth's history.

          

  400. schistoseThe texture of a rock in which visible platy or needle-shaped minerals have grown essentially parallel to each other under the influence of directed pressure.

          

  401. phylliteMineral with the formula CaCO3.

          

  402. eraMajor subdivision of the standard geologic time scale (e.g., Mesozoic Era).

          

  403. correlationIn geology, correlation usually means determining time equivalency of rock units. Rock units may be correlated within a region, a continent, and even between continents.

          

  404. aseismic ridgeThe transformation of preexisting rock into texturally or mineralogically distinct new rock as a result of high temperature, high pressure, or both, but without the rock melting in the process.

          

  405. nonmetallic lusterThe total number of protons in an atom.

          

  406. coalA sedimentary rock formed from the consolidation of plant material. It is rich in carbon, usually black, and burns readily.

          

  407. ice sheetA glacier covering a large area (more than 50,000 square kilometers) of land.

          

  408. oil shaleAsphalt-cemented sand deposit.

          

  409. geyserA broad, flat-topped hill bounded by cliffs and capped with a resistant rock layer.

          

  410. mud crackPolygonal crack formed in very fine grained sediment as it dries.

          

  411. regional metamorphismThe transformation of preexisting rock into texturally or mineralogically distinct new rock as a result of high temperature, high pressure, or both, but without the rock melting in the process.

          

  412. seismic reflectionChange in direction of waves due to slowing as they enter shallow water. (End Chapter 14)

          

  413. erraticAn ice-transported boulder that does not derive from bedrock near its present site.

          

  414. geophysicsThe application of physical laws and principles to a study of Earth.

          

  415. travel-time curveA plot of seismic-wave arrival times against distance.

          

  416. mesaA broad, flat-topped hill bounded by cliffs and capped with a resistant rock layer.

          

  417. covalent bondingA subsurface zone in which rock openings are generally unsaturated and filled partly with air and partly with water; above the saturated zone.

          

  418. dolomiteA sedimentary rock composed mostly of the mineral dolomite.

          

  419. chain silicate structureSilicate structure in which two of each tetrahedron's oxygen ions are shared with adjacent tetrahedrons, resulting in a chain of tetrahedrons.

          

  420. crystalline textureArrangement of various faces on a crystal in a definite geometric relationship to one another.

          

  421. oblique-slip faultLarge fan-shaped pile of sediment that usually forms where a stream's velocity decreases as it emerges from a narrow canyon onto a flat plain at the foot of a mountain range.

          

  422. oreAn electrically charged atom or group of atoms.

          

  423. electronParallel alignment of textural and structural features of a rock.

          

  424. wave heightThe vertical distance between the crest (the high point of a wave) and the trough (the low point).

          

  425. flash floodMechanical weathering of rock by freezing water.

          

  426. ionThe central zone of Earth.

          

  427. AquiferA thick shell of rock that separates Earth's crust above from the core below.

          

  428. isoclinal foldUnderground accumulation of oil.

          

  429. specific gravityThe ratio of the mass of a substance to the mass of an equal volume of water, determined at a specified temperature.

          

  430. radial patternA drainage pattern in which streams diverge outward like spokes of a wheel.

          

  431. parabolic duneA deeply curved dune in a region of abundant sand. The horns point upwind and are often anchored by vegetation.

          

  432. alpine glaciationThe loss of the glacial ice or snow by melting, evaporation, or breaking off into icebergs. (Also called wastage). (Begin Chapter 12)

          

  433. recrystallizationA mode of transport that carries sediment downcurrent in a series of short leaps or bounces.

          

  434. pyroxene groupA powder of fine fragments of rock produced by glacial abrasion.

          

  435. jointA place where water flows naturally out of rock onto the land surface.

          

  436. Mohorovicˇic´ discontinuity (Moho)The boundary separating the crust from the mantle beneath it (also called Moho),.

          

  437. numerical (or absolute) ageAge given in years or some other unit of time.

          

  438. fold and thrust beltsA medium-grained sedimentary rock (grains between 1/16 mm and 2 mm) formed by the cementation of sand grains.

          

  439. longitudinal dune (seif)In mass wasting, movement along a curved surface in which the upper part moves vertically downward while the lower part moves outward. Also called a slump.

          

  440. gravelRounded particles coarser than 2 mm in diameter.

          

  441. fossil assemblageAn irregular line marking the highest level to which the winter snow cover on a glacier is lost during a melt season. (Also called snow line.)

          

  442. crystallineDescribing a substance in which the atoms are arranged in a regular, repeating, orderly pattern.

          

  443. B horizon (zone of accumulation)A representation of a portion of Earth in a vertical plane.

          

  444. crustal reboundThe process whereby the minerals that crystallize at a high temperature in a cooling magma move downward in the magma chamber because they are denser than the magma.

          

  445. beddingAn arrangement of layers or beds of rock. (Begin Chapter 6)

          

  446. debris slideRapid movement of debris as a coherent mass.

          

  447. Rayleigh waveA type of surface seismic wave that behaves like a rolling ocean wave and causes the ground to move in an elliptical path.

          

  448. rock avalancheA very rapidly moving, turbulent mass of broken-up bedrock.

          

  449. playa lakeA shallow temporary lake (following a rainstorm) on a flat valley floor in a dry region.

          

  450. desertA region with low precipitation (usually defined as less than 25 cm per year).

          

  451. frost actionMechanical weathering of rock by freezing water.

          

  452. magnetiteiron oxide that is attracted to a magnet.

          

  453. sea-floor spreadingThe concept that the ocean floor is moving away from the mid oceanic ridge and across the deep ocean basin, to disappear beneath continents and island arcs.

          

  454. sea cliffSteep slope that retreats inland by mass wasting as wave erosion undercuts it.

          

  455. shear stressStress due to forces that tend to cause movement or strain parallel to the direction of the forces.

          

  456. terminusA body of till either being carried on a glacier or left behind after a glacier has receded.

          

  457. arch (sea arch)The oldest eon of Earth's history.

          

  458. mid-oceanic ridgeA giant mountain range that lies under the ocean and extends around the world.

          

  459. muscoviteLine dividing one drainage basin from another.

          

  460. open foldA fold with gently dipping limbs.

          

  461. pyroclastic flowTurbulent mixture of pyroclastics and gases flowing down the flank of a volcano.

          

  462. equilibrium lineA mine in which the valuable material is exposed at the surface by removing a strip of overburden.

          

  463. feldspar groupGroup of most common minerals of Earth's crust. All feldspars contain silicon, aluminum, and oxygen and may contain potassium, calcium, and sodium.

          

  464. icebergBlock of glacier-derived ice floating in water.

          

  465. Pleistocene EpochMovement within a glacier in which the ice is not fractured.

          

  466. positive magnetic anomalyGreater than average strength of the earth's magnetic field.

          

  467. incised meanderA meander that retains its sinuous curves as it cuts vertically downward below the level at which it originally formed.

          

  468. sheet silicate structureSilicate minerals that are structured so that none of the oxygen atoms are shared by silica tetrahedrons.

          

  469. pedimentThe solid material that precipitates in the pore space of sediments, binding the grains together to form solid rock.

          

  470. zone of ablationPortion of a continent that has been structurally stable for a prolonged period of time.

          

  471. isolated silicate structureA feature found within sedimentary rocks, usually formed during or shortly after deposition of the sediment and before lithification.

          

  472. ferromagnesian mineralA mine in which the valuable material is exposed at the surface by removing a strip of overburden.

          

  473. streamA moving body of water, confined in a channel and running downhill under the influence of gravity.

          

  474. stream gradientDownhill slope of a stream's bed or the water surface, if the stream is very large.

          

  475. ionic bondingBonding due to the attraction between positively charged ions and negatively charged ions.

          

  476. perched water tableThe upper surface of the zone of saturation.

          

  477. potholeUnsorted and unlayered rock debris carried by a glacier.

          

  478. confining pressurePressure applied equally on all surfaces of a body; also called geostatic or lithostatic pressure.

          

  479. contour currentA bottom current that flows parallel to the slopes of the continental margin (along the contour rather than down the slope).

          

  480. rock-basin lake (tarn)A drainage pattern in which tributaries of a river change direction and join one another at right angles.

          

  481. sinkholeA closed depression found on land surfaces underlain by limestone.

          

  482. bedding planeA nearly flat surface separating two beds of sedimentary rock.

          

  483. fracture zoneMajor line of weakness in Earth's crust that crosses the mid-oceanic ridge at approximately right angles.

          

  484. suspect terraneA terrane that may not have formed at its present site.

          

  485. sedimentLoose, solid particles that can originate by (1) weathering and erosion of preexisting rocks, (2) chemical precipitation from solution, usually in water, and (3) secretion by organisms.

          

  486. Quaternary PeriodThe youngest geologic period; includes the present time.

          

  487. strikeBreaking waves.

          

  488. deltaA fracture in bedrock along which movement has taken place.

          

  489. unconfined aquiferA partially filled aquifer exposed to the land surface and marked by a rising and falling water table.

          

  490. exfoliation domeA hill or mountain constructed by the extrusion of lava or rock fragments from a vent. (End Chapter 4)

          

  491. stockA small discordant pluton with an outcropping area of less than 100 square kilometers.

          

  492. P waveA compressional wave (seismic wave) in which rock vibrates parallel to the direction of wave propagation.

          

  493. seamountSediment composed of particles with a diameter between 1/16 mm and 2 mm.

          

  494. pluvial lakeA lake formed during an earlier time of abundant rainfall.

          

  495. silicon-oxygen tetrahedronFour-sided, pyramidal object that visually represents the four oxygen atoms surrounding a silicon atom; the basic building block of silicate minerals. Also called a silica tetrahedron or a silicon tetrahedron.

          

  496. sandAn electrically charged atom or group of atoms.

          

  497. matrixA place where water flows naturally out of rock onto the land surface.

          

  498. valley glacierA glacier confined to a valley. The ice flows from a higher to a lower elevation.

          

  499. subduction zoneMajor line of weakness in Earth's crust that crosses the mid-oceanic ridge at approximately right angles.

          

  500. tillUnsorted and unlayered rock debris carried by a glacier.

          

  501. contactBoundary surface between two different rock types or ages of rocks.

          

  502. atollFine-grained material found in the pore space between larger sediment grains.

          

  503. Benioff zoneDistinct earthquake zone that begins at an oceanic trench and slopes landward and downward into Earth at an angle of about 30° to 60°.

          

  504. reservoir rockA rock that is sufficiently porous and permeable to store and transmit petroleum.

          

  505. igneous rockA rock that is sufficiently porous and permeable to store and transmit petroleum.

          

  506. stream velocityOriginal rock before being metamorphosed.

          

  507. tsunami (seismic sea wave)Huge ocean wave produced by displacement of the sea floor; also called seismic sea wave.

          

  508. ophioliteA metamorphic rock characterized by coarse-grained minerals oriented approximately parallel.

          

  509. petrified woodA stream that exhibits a delicate balance between its transporting capacity and the sediment load available to it.

          

  510. recumbent foldThe solid material that precipitates in the pore space of sediments, binding the grains together to form solid rock.

          

  511. clay mineralA hydrous aluminum-silicate that occurs as a platy grain of microscopic size with a sheet silicate structure.

          

  512. parent rockA stream bar (see definition) deposited on the inside of a curve in the stream, where the water velocity is low.

          

  513. pressure releaseA significant type of mechanical weathering that causes rocks to crack when overburden is removed.

          

  514. intensityJoints oriented in one direction approximately parallel to one another.

          

  515. mass wastingOn minerals, extremely straight, parallel lines. (End Chapter 2)

          

  516. differential stressWhen pressures on a body are not of equal strength in all directions.

          

  517. loessTraces of plants or animals preserved in rock.

          

  518. metamorphismThe transformation of preexisting rock into texturally or mineralogically distinct new rock as a result of high temperature, high pressure, or both, but without the rock melting in the process.

          

  519. sedimentary structureA feature found within sedimentary rocks, usually formed during or shortly after deposition of the sediment and before lithification.

          

  520. A horizon (zone of leaching)Rounded by weathering from an initial blocky shape.

          

  521. calciteMineral with the formula CaCO3.

          

  522. marbleA fine-grained sedimentary rock (grains finer than 1/16 mm in diameter) formed by the cementation of silt and clay (mud). Shale has thin layers (laminations) and an ability to split (fissility) into small chips.

          

  523. residual soilUpper part of a glacier in which there is no plastic flow.

          

  524. coastA fracture or crack in bedrock along which essentially no displacement has occurred.

          

  525. shaleA fine-grained sedimentary rock (grains finer than 1/16 mm in diameter) formed by the cementation of silt and clay (mud). Shale has thin layers (laminations) and an ability to split (fissility) into small chips.

          

  526. cementationBoundary surface between two different rock types or ages of rocks.

          

  527. lithificationIciclelike pendant of dripstone formed on cave ceilings.

          

  528. flood plainA broad strip of land built up by sedimentation on either side of a stream channel.

          

  529. concretionHard, rounded mass that develops when a considerable amount of cementing material precipitates locally in a rock, often around an organic nucleus.

          

  530. P-wave shadow zoneThe region on Earth's surface, 103° to 142° away from an earthquake epicenter, in which P waves from the earthquake are absent.

          

  531. accreted terraneTerrane that did not form at its present site on a continent.

          

  532. ultramafic rockA body of rock of considerable thickness that has a recognizable unity or similarity making it distinguishable from adjacent rock units. Usually composed of one bed or several beds of sedimentary rock, although the term is also applied to units of metamorphic and igneous rock. A convenient unit for mapping, describing, or interpreting the geology of a region.

          

  533. submarine canyonV-shaped valleys that run across the continental shelf and down the continental slope.

          

  534. cementA glacier covering a relatively small area of land but not restricted to a valley.

          

  535. debris avalancheVery rapid and turbulent mass wasting of debris, air, and water.

          

  536. dikeA region with low precipitation (usually defined as less than 25 cm per year).

          

  537. seismographA seismometer with a recording device that produces a permanent record of Earth motion.

          

  538. Proterozoic EonEon of Precambrian time.

          

  539. braided streamiron oxide that is attracted to a magnet.

          

  540. shield volcanoAny of the layers of soil that are distinguishable by characteristic physical or chemical properties.

          

  541. suspended loadSediment in a stream that is light enough in weight to remain lifted indefinitely above the bottom by water turbulence.

          

  542. transportationSoil not formed from the local rock but from parent material brought in from some other region and deposited, usually by running water, wind, or glacial ice.

          

  543. reverse faultA free-falling mass of debris.

          

  544. structural domeA structure in which beds dip away from a central point.

          

  545. graniteA felsic, coarse-grained, intrusive igneous rock containing quartz and composed mostly of potassium- and sodium-rich feldspars.

          

  546. plagioclase feldsparA feldspar containing sodium and/or calcium in addition to aluminum, silicon, and oxygen.

          

  547. erosionAn electrically charged atom or group of atoms.

          

  548. reliefAn arrangement of layers or beds of rock. (Begin Chapter 6)

          

  549. ripple markAny of the small ridges formed on sediment surfaces exposed to moving wind or water. The ridges form perpendicularly to the motion.

          

  550. negative gravity anomalyA major concentration of earthquakes and composite volcanoes that runs through the Mediterranean Sea, crosses the Mideast and the Himalaya, and passes through the East Indies.

          

  551. magnetic reversalA broad, flat-topped hill bounded by cliffs and capped with a resistant rock layer.

          

  552. intermediate rockRock with a chemical content between felsic and mafic compositions.

          

  553. mantleA thick shell of rock that separates Earth's crust above from the core below.

          

  554. seismic refractionSubmarine ridge with which no earthquakes are associated.

          

  555. Mesozoic EraEon of geologic time. Includes all time following the Precambrian.

          

  556. stackA circular reef surrounding a deeper lagoon.

          

  557. ground moraineA blanket of till deposited by a glacier or released as glacier ice melted.

          

  558. barchanFine-grained material found in the pore space between larger sediment grains.

          

  559. bermPlatform of wave-deposited sediment that is flat or slopes slightly landward.

          

  560. disconformityCoarse-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar and the rest is ferromagnesian minerals.

          

  561. magmatic arcA line of batholiths or volcanoes. Generally the line, as seen from above, is curved.

          

  562. uniformitarianismA soil layer composed of incompletely weathered parent material.

          

  563. kettleA depression caused by the melting of a stagnant block of ice that was surrounded by sediment.

          

  564. fine-grained rockSilica-deficient igneous rock with a relatively high content of magnesium, iron, and calcium.

          

  565. roundingThe grinding away of sharp edges and corners of rock fragments during transportation.

          

  566. magmaSee rock-basin lake.

          

  567. artesian wellSoil that develops directly from weathering of the rock below.

          

  568. tilliteCapable of being molded and bent under stress.

          

  569. thrust faultA reverse fault in which the dip of the fault plane is at a low angle to horizontal. (End Chapter 15)

          

  570. volcanic brecciaRock formed from large pieces of volcanic rock (cinders, blocks, bombs).

          

  571. sedimentary brecciaTotal area drained by a stream and its tributaries.

          

  572. butteObservations or measurements used by scientists to test hypotheses.

          

  573. batholithA large discordant pluton with an outcropping area greater than 100 square kilometers.

          

  574. headlandThe opening in Earth's surface through which a volcanic eruption takes place.

          

  575. moment magnitudeAn earthquake magnitude calculated from the strength of the rock, surface area of the fault rupture, and the amount of rock displacement along the fault.

          

  576. cirqueA steep-sided, amphitheater-like hollow carved into a mountain at the head of a glacial valley.

          

  577. baymouth barA ridge of sediment that cuts a bay off from the ocean.

          

  578. theoryAn explanation for observed phenomena that has a high possibility of being true.

          

  579. oxbow lakeA crescent-shaped lake occupying the abandoned channel of a stream meander that is isolated from the present channel by a meander cutoff and sedimentation.

          

  580. country rockA rock formed or apparently formed from solidification of magma.

          

  581. continental riseA stream bar (see definition) deposited on the inside of a curve in the stream, where the water velocity is low.

          

  582. transform faultA fine-grained, mafic, igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.

          

  583. rip currentNarrow currents that flow straight out to sea in the surf zone, returning water seaward that has been pushed ashore by breaking waves.

          

  584. obsidianPoint of land along a coast.

          

  585. crude oilA volcano constructed of loose rock fragments ejected from a central vent.

          

  586. sand duneA body of till either being carried on a glacier or left behind after a glacier has receded.

          

  587. metamorphic rockRock that has formed from (1) lithification of any type of sediment, (2) precipitation from solution, or (3) consolidation of the remains of plants or animals.

          

  588. volcanoA hill or mountain constructed by the extrusion of lava or rock fragments from a vent. (End Chapter 4)

          

  589. flowA type of movement that implies that a descending mass is moving downslope as a viscous fluid.

          

  590. weatheringAn explanation for observed phenomena that has a high possibility of being true.

          

  591. longshore driftMovement of sediment parallel to shore when waves strike a shoreline at an angle.

          

  592. sedimentary rockA feature found within sedimentary rocks, usually formed during or shortly after deposition of the sediment and before lithification.

          

  593. streakChange in size (volume) or shape of a body (or rock unit) in response to stress.

          

  594. rigid zoneUpper part of a glacier in which there is no plastic flow.

          

  595. AblationUnsorted and unlayered rock debris carried by a glacier.

          

  596. lateral moraineA low ridgelike pile of till along the side of a glacier.

          

  597. fine-grained rockOriginal rock before being metamorphosed.

          

  598. siltA small rock island that is an erosional remnant of a headland left behind as a wave-eroded coast retreats inland.

          

  599. sandstoneA medium-grained sedimentary rock (grains between 1/16 mm and 2 mm) formed by the cementation of sand grains.

          

  600. dioriteCoarse-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar and the rest is ferromagnesian minerals.

          

  601. potassium (orthoclase) feldsparA feldspar with the formula KAlSi3O8.

          

  602. saturated zoneA rock containing organic matter that is converted to petroleum by burial and other postdepositional changes.

          

  603. epicenterA ferromagnesian mineral with the formula (Fe, Mg)2SiO4.

          

  604. talusA small discordant pluton with an outcropping area of less than 100 square kilometers.

          

  605. lithosphereThe rigid outer shell of Earth, 70 to 125 or more kilometers thick.

          

  606. Richter scaleA numerical scale of earthquake magnitudes.