fig. 14-1 Average chemical composition of the earth's crust. Percentages are by mass.

fig. 14-2 The silicon-oxygen tetrahedron is the fundamental unit in all silicate structures. Dashed lines show the tetrahedral form of SiO₄^4-; solid lines are bonds between the ions.

fig. 14-3 Some crystal forms found in minerals.

fig. 14-4 (a) Mica has one direction of cleavage and fractures irregularly if broken across its cleavage plane. (b) Feldspar has two perpendicular cleavage planes and fractures irregularly if broken across them. (c) Calcite has three directions of cleavage that are not perpendicular to each other.

fig. 14-5 Some major earthquakes and their magnitudes on the Richter scale. The San Francisco and Tokyo earthquakes, together with the fires that followed them, led to the almost complete destruction of those cities. Over a quarter of a million people died in the Tangshan earthquake.

fig. 14-6 How an earthquake occurs. (a) The sides of a fault between crustal blocks have stuck together, preventing movement even though the forces (arrows) on them remain active. (b) As time goes on, stresses build up in the adjacent blocks, which deform as a result. (c) When the locked-in stresses become too great, the blocks suddenly shift to release them. The stored-up elastic energy powers the vibrations that constitute an earthquake. The focus of an earthquake is the place where the crustal blocks moved; the epicenter of the quake is the point on the surface directly over the focus.

fig. 14-7 Earthquakes are expected during the next 100 years in the parts of the United States shown in color. The darker the color, the greater the likely damage. The earthquake probability is especially high in California because locked-in stresses have built up in many of the thousands of faults that riddle the region. The most severe earthquakes in U.S. history were a trio that occurred in the winter of 1811-1812 at New Madrid in southeastern Missouri, which is in the dark spot south of the Great Lakes in this map. The quakes were felt over most of the country east of the Rockies; the vibrations set church bells ringing as far away as Boston.

fig. 14-8 (a) Earthquake body waves travel through the earth's interior. P waves are longitudinal, like sound waves. S waves are transverse, like waves in a stretched string. P waves can move through a liquid; S waves cannot. (b) Earthquake surface waves travel on the earth's surface. Love waves are transverse, with their vibrations parallel to the surface. Rayleigh waves involve orbital motions, like water waves. All the waves shown here are moving from left to right. The arrows show the directions in which the rock particles move.

fig. 14-9 Earthquake waves are detected by instruments called seismographs. This is a record of waves from an earthquake that occurred about 5000 km from the location of seismograph.

fig. 14-10 How earthquake waves travel through the earth. The existence of a shadow zone where neither P nor S waves arrive is evidence for a core. The inability of S waves to get through the core suggests that at least the outer part of it is liquid. The inner core is believed to consist of iron crystals.

fig. 14-11 Structure of the earth. The mantle constitutes 80 percent of the earth's volume and about 67 percent of its mass.

fig. 14-12 The Mohorovicic discontinuity separates the earth's crust from the mantle below it. The crust is thicker and has a different composition under the continents than under the oceans.

fig. 14-13 The earth's magnetic field originates in electric currents in its core of molten iron. The magnetic axis is tilted by 11° from the axis of rotation, so magnetic compasses do not point to true north.

fig. 14-14 Successive stages in the development of a river valley.

fig. 14-15 Parallel ridges and valleys produced by stream erosion in tilted layers of hard and soft rocks. Soft layers underlie the valleys; hard layers, the ridges. Landscapes and rock structures of this sort are typical of the Appalachian Mountains.

fig. 14-16 Cross sections through a landscape underlain by porous material. The position of the water table is shown (a) just after a heavy rain, (b) several days later, and (c) after a prolonged drought. The spring, the stream, and the upper well would be dry during the drought.

fig. 14-17 Cross section of a steep, rocky shoreline.

fig. 14-18 Cross section of a volcano. During explosive eruptions much liquid rock is blown into fragments when it emerges. Deposits of the finer material may form the rock tuff, and deposits of the coarser material may form a kind of conglomerate called volcanic breccia. In the volcano shown, lava flows (solid color) alternate with beds of tuff and volcanic breccia.

fig. 14-19 The principal earthquake (light color) and volcanic (dark color) regions of the world.

fig. 14-20 A batholith and associated dikes and sills; a laccolith and a volcano are also shown.

fig. 14-21 The rock cycle. Depending upon circumstances, different paths are possible, including the conversion of one kind of metamorphic rock into another.