250 



INDEX TO PART IV. 



Porphyries, diversity of . 



" origin of 

 Porphyritic diabase, 



" diorite, . 



" felsite, . 



Porphyrite, .... 

 Porphyry breccia, . 



" conglomerate, . 

 Portland sandstone, 

 Prehnite, .... 



Pressure cleavage in mica. 

 Pressure under which granites crys- 

 tallized, . . . .183 

 Primal rocks, .... 

 Prochlorite, .... 

 Protogene, .... 



" gneiss. 

 Pudding granite. 

 Purple copper. 

 Pseudo-porphyritic granite, 

 Psilomelane, .... 



Pyrite, 



Pyroxene, .... 

 Pyroxene and hornblende, relations 



of, 



Pyroxene crystals in rock sections 

 Pyrolusite, .... 

 Pyrrhotite, .... 



Quartz, 



" diorite, 

 Ouartz-free orthoclase porphyry, 

 Ouartzite, .... 



Quartz porphyry, 



" schist, 



" schist, half fragmental, 



" veins, .... 



Red diorite, .... 



" granite 



" sandstone, 

 Remarks on basic eruptive rocks, 



'* on greenstones, 

 Rhodochrosite, 



Rhodonite, .... 

 Ripidolite, .... 

 Rock analysis, 



" methods of 



Roofing slate, 



Rose quartz, .... 

 Roxbury granite, 

 Rutile, 



186 

 177 



154 

 160 

 177 

 160 

 186 

 186 



239 

 112 



193 



140 



119 



201 



215 



203 



29 



196 



48 



31 



54 



57 

 56 

 46 

 30 



49 

 229 

 187 

 223 

 178 

 223 

 238 



50 



165 

 197 



239 

 170 



233 



131 



58 



118 



143 

 6 



237 

 49 

 195 



45 



Salts in solution, in rock cavities, 



181, 183, 192, 202 



Saussurite, 92 



Scenery among slaty rocks, . . 238 

 Schistose, structure-causes of 210, 212 



