CONTENTS OF PART I . Page. Introduction 17 Cascade Range 17 Limits 17 Foundation 17 Eocene history 19 Miocene history 20 Union Peak 20 Mount Thielsen 21 Mount Mazama 21 General features 21 Lavas 23 Andesites 23 Watchman area 25 Castle Creek area 25 Munson Point area 25 Union Peak area 26 Eagle Crags area 26 Dutton Cliff area 27 Sentinel Rock area 27 Round Top area 28 Steel Bay area 29 Wizard Island 29 Andesitic dikes 30 Basalts 31 Timber Crater flow 32 Desert Cone and Red Cone flows 32 Bald Crater flow 33 Crater Peak flow 33 Other flows 34 Dacites 34 Sun Creek flow 35 Cloud Cap flow 35 Grouse Hill flow 36 Llao Rock flow 36 Wineglass flow 37 Cleetwood Cove flow 38 Dacitic dikes 39 Dacitic pumice 39 Mount Mazama - Continued. Page. Glaciation , 41 Original condition 44 Development 45 Destruction of Mount Mazama and formation of the caldera 46 Crater Lake 50 Temperature 50 Changes of water level 53 Evaporation 57 Inflow 59 Outlet 60 CONTENTS OF PART II. Page. Hypersthene-andesites 69 Mineral components 69 Plagioclase 69 Pyroxene , 78 Hypersthene 78 Augite 82 Accessory minerals 83 Classification of andesites 83 Hyalopilitic type 84 Hypocrystalline type 85 Subtype A 86 Subtype B 87 Holocrystalline type 88 Dacitic type 91 Uncertain types 91 Andesite dikes 92 Chemical analyses 94 . Secretions in andesites 95 Hypersthene-dacites 99 Mineral components 100 Feldspar 100 Hornblende 102 Hypersthene 104 Augite 104 Other minerals 104 Distribution and description of dacite masses 105 Llao Rock flow 105 Vitrophyric dacite 105 Lithoidal dacite 106 Spherulitic dacite 107 Nodular secretions 109 Grouse Hill flow 111 Cleetwood Cove flow 112 Wineglass flow 113 Cloud Cap flow 114 Sun Creek flow 116 9255 No. 3 02


5 CONTENTS OF PART II. Hypersthene-dacites - Continued. Page. Dacite tuff 121 Dacite dikes 121 Dacitic ejectamenta 123 Pumice 124 Dark-colored secretions 125 Light-colored granophyric secretions 130 Secretions with basalt-like structure 139 Chemical analyses . 140 Basalts 141 Interstitial basalts 141 Mineral components 142 Feldspar 142 Augite 143 Hypersthene 143 Olivine 144 Magnetite 145 Hypersthene, apatite, and pseudobrookite crystals 145 Apatite 146 Hypersthene 146 Pseudobrookite 147 Fluidal-interstitial basalts 148 Porphyritic-interstitial basalts 152 Andesitic basalts 156 Type A 157 Type B 158 Type C 159 Type D 159 Chemical analyses 161 Concluding remarks on the basalts 162 Table of thin sections, with new and old numbers 164