Hall, Sir James, experiments, 135, 139 Heterocercal tails of fishes, 48 Homocercal tails, 48 Hornblende, 14 Hornblende slate, 20, 32 Hydrogen, 11 Hypersthene, 15 Hypersthene rock, 17, 25 I. Icebergs-- how formed, 124 earthy materials in, 125 motion of, 125 size and number of, 125 effect in distributing drift, 126 grooving the surface, 126 Iceland spar, 19 Iceland, volcanic eruption in, 26 Ichthyosaurus, 50 Igneous causes, 127 Iguanodon, 51 Inclined position of strata produced by upheaval, 70, 140 Increase of temperature below the surface, 127 Iron, 12 J. Jasper, 14 Jorullo, 131 K. Kilauea, 26, 142 L. Lakes, filling up of, 76, 113 Lava, 17, 25, 137 varieties of, 25 tertiary, 27 elastic vapors contained in, 130, 132 great quantity of modern, 26 Lead-bearing strata, 35, 40 Lepidodendron, 46 Lias, 19, 49 Limestone, 15, 19 as a primary rock, 25 metalliferous, 40 Local changes of climate, 90 M.