Declivity, General influence of, upon erosion, 102 of stream beds, relation to corrasion, 112 , relation to transportation, 108 , Relation of, to quantity of water, 113 Declivities, Influence of unequal, on divides, 140 Degradation (see Erosion), 99, 115 Delesse on contraction of igneous rocks in cooling, 76 Densities of igneous rocks, 75 of sedimentary rocks, 77 Density a condition of laccolitic intrusion, 73, 74 of porphyritic trachyte, 77 Denudation (see Erosion), 99, 115 of laccolites, 21 Deposition by running water, 111 Diameters of laccolites, 92 Dike near Mount Ellsworth, 59 Dikes and sheets defined, 20 , Flat-topped, 28 of Mount Ellsworth, 23 of Mount Holmes, 28 , Relation of, to strains, 96 Dinah Creek Pass, 3 Dirty Devil River, Flood-plains of, 131 Distances, Table of, 17 Distribution of laccolites, Horizontal, 20, 30 , Vertical, 21, 56 Divides in bad-lands, Rounding of, 122 , Instability of, 139 , Law of, 116 , Stability of, 138 Drainage lines, Instability of, 125 , Stability of, 124 , Systems of, 124, 143 Dutton, Capt. C. E., on the intrusive rocks, 61 Economic geology, 151 Elk Mountains, 69 Ellen Mount (see Mount Ellen). Ellsworth Mount (see Mount Ellsworth). Energy of muddy streams, 108 streams, how measured, 106 Equal action, Principle of, 123 Erosion, Conditions which control, 102 , Influence of climate upon, 103 , Influence of declivity upon, 102 Erosion, Influence of rock texture upon, 103 , Influence of vegetation upon, 104 of Mount Ellsworth, 25 , Principles of, 99 , Processes of, 99 Farming lands, 152 Faults on Mount Ellsworth, 23 Mount Holmes, 28 , Region of, 12, 15 Fish Lake Valley, Structure of, 14 Fissure veins limited in depth, 82 not found in the Henry Mountains, 83, 151 Flaming Gorge Group, 6 Flat-topped dikes, 28 Flexure of rocks, Conditions of, 83 Flood-plain defined, 127 Flow of streams, Friction of, 107, 109 Folds, The Great, 10, 11, 85 Forces which produce laccolitic arches, 87 Form of laccolites, 55 Frost, 104 Friction of flow of streams, 107, 109 Geikie laccolite, 41 Gold and silver, 151 Granite, Eruptive, 70 Graves, Mr. Walter H., 1 Gray Cliff Group, 6 Grazing lands, 152 Heights, 3, 117 Henry, Prof. Joseph, 1 Henry Mountains, Altitudes of the, 2, 117 caused by resistance of trachyte to erosion, 25, 35 , Contributions of the, to the principles of erosion, 99 , Detailed description of the, 22 , Drainage of the, 144 , Economic value of the, 152 , Planation in the, 127, 149 , Relation of vegetation to type of sculpture in the, 118 , Route of travel to the, 14; their structure laccolitic, 19, 53 Henry’s Fork Group, 4 Hillers, Mount (see Mount Hillers). Hills of planation, 130 Historical note, 66 History of the Colorado Basin, 84 Holmes, Mount (see Mount Holmes).