xiv CONTENTS. 



Obliteration of original characters in tlie process of tlie alteration of Pcridotitcs, 



175. Production of Schistose Structure in, 175. The supposed conversions of 

 Schists into Serpentine, 175. Absence of the Mesh Structure and Chroniite or 

 Picotite in Serpentine due to alteration, 175. F'onuation of Serpentine Vein- 

 stones, 175. Altcrntion minerals in Peridotite, 175. Ground covered by the 

 text, 175. 



SECTION VII. 



Chromite and Picotite. — Their PiElatmns 176-186 



Fischer's observations, 176. Dathe's studies, 176. Thoulet's observations, 



176. Translucency of Chromite first remarked in 1825, by C. H. Pfafp, 176. The 

 writer's observations on some eighty specimens of Chromite, Picotite, and Ores of 

 Iron, 177-180. < Color and lustre of massive Chromite, 180. Hardness and streal< 

 of Chromite and Picotite, 180. Specific gravity of, 180. Coffee-hrowa color of, 

 180. Variability in color of, 180, 181. Observation of translucency, 181. 

 Preparation of specimens, 181. Chemical relations of Chromite and Picotite, 

 181-183. Views of Genth and Rammelsberg on, 183. Microscopic relations of, 

 183, 184. Conclusions regarding mineral species and their variability, 18-4, 185. 

 A natural system in mineralogy, 185. Strange history of a Chromite Analysis, 

 185, 186. Errors in published lists of Analyses, 186. 



SECTION VIII. 



Peridotite. — Its Chemical Characters 186-189 



Designation of the varieties of Peridotite, 186. Specific gravity of, 186, 187. 

 The Carbonaceous Meteorites, 186, As specific gravity decreases, the Iron dimin- 

 ishes and Magnesia increases, 187. Microscopic characters of the Cold-Bokkeveld 

 Meteorite, 186. Percentage of silica in Pallasite, 187; of silica in Peridotite, 

 187, 188. Special case of the Cabarras Meteorite, 187. Percentages of aluminia, 

 iron, lime, and magnesia in Peridotite, 188. The meteoric forms richest in Iron, 188. 

 Alteration leads to decrease in the percentage of Iron, 188. Relation of Picrite 

 to Basalt, 188. Minor elements in Peridotite, 188. Water proportioned to the 

 amount of alteration, 188, 189. General chemical characters of Peridotite, 189. 



SECTION IX. 

 Peridotite. — Its Origin 189-192 



Eruptive occurrence of Peridotite in the Cornwall, Troad, and Lake Superior 

 districts, 189. Relations of Schistose Rocks and Peridotes, 189, 190. Associa- 

 tion of Eruptive and Schistose Rocks, 189. The Schists produced by alteration 

 of Peridotite, 189, 190. Detritus of Eruptive Rocks, 190. Peridotic Volcanoes, 

 190. Expected occurrence of Peridotites, 190; difficulty of the study of, 190. 

 Production of Serpentine by alteration of Peridotite, 190. Migration of mineral 

 matter, 190. Chemical precipitation of Serpentine from ocean waters, 190. Con- 

 fusion between migrated serpentine material and that produced by alteration 

 ill situ, 190. Serpentine question allied to tne phenomena of Eruptive Rocks and 

 Veinstones, 190, 191. No proof that the Canadian Serpentines are stratified 

 sedimentary deposits, 191. Believed inaccuracy of Dr. Hunt's writings, 191. 



