Grand Canyon of the Colorado, iii, 40-3, 140, 230, xiv, 83; conical fragments in, 81; outer and inner gorges, 173; plateau of, 124, 159, 220; Proterozoic strata in, iii, 177; rock pyramids in, xiv, 224-5 Grand Canyon of the Yellowstone, iii, 44, and Pl. 2, p. 48; color of rocks in, 26; youthful valley type, 33; relief model of, xiv, 10 Grand Point Tobacco, xiii, 258 Granite, composition, iii, 308, 326, viii, 192-3; disintegration of, 194; igneous nature, iii, 112; jointing of, xiv, 133; mountain cores of, 110-11; occurrence and production, iii, 371; plutonic rock, 13, xiv, 18; weathering of, iii, 22, 27-8, 32 (Pl. 1), xiv, 78-9; wells in, 137 Grapes, acids of, viii, 223; origin and antiquity, xiii, 225, 324-5; true berries, 54; water content, viii, 365 Grape Sugar, viii, 224-5; polarization of light by, iv, 356 Grapevines, xiii, 27, 28 Graphite, iii, 331, viii, 43; in Archeozoic rocks, iii, 173, 249-50; Rhode Island beds, 345; use and production, vii, 308-9, xvi, 190 Graptolites, iii, 259, 266 (fig.), 267 Grasp, in infants, ix, 349, xv, 61; of man, ix, 67-8; grasping importance and organs of, 82; reflex processes in, 157, 349 Grasping Reflex, xi, 40-5, 59 Grass, blue-eyed, xiii, 189; leaves of, 176; monocotyledon, 178; veins, 32 (see also Grass Family) Grasses, dominant on prairies, xiii, 350, 374; evolution, iii, 251, 257; fertilization, xiii, 148; first appearance, 319; true and incorrect, 179, 180; water requirements, xiv, 381 Grass Family, xiii, 179, 181-3 Grasshoppers, xii, 108-10; jaws of, 100 Grasslands, xiii, 373-7; contests with forests, 348-9, 368 (illus.), 374-5, xiv, 380-1; distribution of, 380, 381; economic importance, 383-4; vegetation of, 380, 381 Gratitude, sentiment of, xi, 147 Graupel, i, 107, 373 Gravel, rocks formed from, iii, 13, 53 (see Conglomerate); sedimentary rock, xiv, 18 Grave Sacrifice, custom of, xv, 336 Graves, Robert, x, 112 Graves Disease, x, 351-2 Gravitation, universal, discovery and laws, ii, 63-72, iv, 20, 95-8, xvi, 115-16; Einstein theory, ii, 79-82; magnetic force compared with, iv, 249-50; nature of, ii, 78; things unexplained by Newton's laws, 73-4, 78-82; various applications of Newton's laws, 77, 78, 375, 380 (see also Gravity) Gravitation Units, iv, 64, 70 Gravity, ii, 63-4, 69, iv, 65, 109; acceleration of, 65; center of, 99-101; direction of earth's, 98-9; force in falling bodies, 42, 65, xvi, 32; gyroscope and, v, 335, 336, 337-9; Huygens's studies, ii, 58; on asteroids, 257; on moon, 199, 204; on sun, 168; Richer's observations, 59; water-power due to, v, 76-7, 139; weight due to, iv, 58, 74, 109 Gravity Battery, iv, 297, vi, 137, 140-1 Gravity Faults, xiv, 115