396 



INDEX 



Nepheline as a rock constituent, 18 

 roeks, the, chemical composition 

 of, classification of, colors of, 

 mineral composition of, no- 

 menclature of, structure of, 

 97 

 (Elaeolite) syenites, 73 



chemical composition of, 74= 

 classification of, 75 

 colors of, 74 



mineral composition of, 73 

 nomenclature of, 75 

 structure of, 74 

 weathering of, 196 

 Nephelinite, 98 

 Nevadite defined, 68 

 Nile, delta of, 309 



vallej, cause of fertility, 313 

 Nitrates in soils, 360, 361 



origin of, 361 

 Nitric acid in the atmosphere, 155 

 Nitrogen, effects of on rocks, 154 



of soils, 360 

 Norites, 82 

 Novaeulite, 104 

 Nummulitic limestone, 125 



Ohsidian defined, 68 



Oligoelase, as a rock constituent, 16 



weathering of, 228 

 Olivine, alteration of, 23 



as a rock constituent, 22 

 Oolitic limestone, 125 

 origin of, 105 

 structure of, 126 

 Opal, 103 

 Ophiolite, 108 

 Ophite, 84 

 Organic acids, effects of, 174 



matter in soils, 314 

 Original constituents of rocks, 10 

 Orthoclase as a rock constituent, 14 

 porphyries, 71 



chemical composition of, 71 

 classification of, 71 

 colors of, 71 

 nomenclature of, 71 

 structure of, 71 

 Orthophyr defined, 71 

 Osar, see glacial deposits, 278, 338 

 Ouachitite, 75 

 Overwash plains, 344 

 Oxidation, 165 



Oxygen, as a constituent of the 

 earth's crust, 5 

 of the atmosphere, 158 



Paludal deposits, 324 

 Pantellerite defined, 68 



Peat, composition and origin, 129 

 Pebbles, normal form of, 331 

 Pegmatite defined, 63 

 Pelites, 117 

 Peperino, 122 



Peridotite-Limburgite group, 89 

 Peridotites, the, 90 



chemical composition of, 90 



classification of, 90 



colors of, 91 



mineral composition of, 90 



nomenclature of, 91 



structure of, 91 

 Phonohtes, the, 75 



chemical composition of, 76 



classification of, 76 



colors of, 76 



mineral composition of, 75 



nomenclature of, 76 



structure of, 76 

 Phonolite, Bohemia, analyses of, 198 



weathering of, 197 

 Phosphates, 111 

 Phosphatic group of rocks, 131 



sandstone, 111, 132 

 Phosphorite, 111 

 Phosphorus as a constituent of the 



earth's crust, 7 

 Phyllite, 148 



Physical and chemical properties of 

 of rocks, 30 



manifestations of weathering, 

 227 

 Picrite, 92 



porphyrites, 92 

 Pisolitic limestone, 125 

 Plagioelase feldspars, 15 

 Plant life, effect on rocks, 378 

 Plants and animals, action of, 180 

 Plutonic rocks defined, 56 

 Porphyrites, the, 78 



chemical composition of, 78 



classification of, 78 



colors of, 78 



mineral composition of, 78 



structure of, 78 

 Porphyritic structure, cause of, 58 

 Porphyroid, 146 

 Potassium as a constituent of the 



earth's crust, 6 

 Potomac clays, mechanical analyses 



of, 301 

 Potstone, 95 

 Primary rocks, 47 

 Protogine defined, 63 

 Propyllite, 80 

 Proterobase, 84 

 Psammites, 113 



