CHAPTER XXXV. METAMORPHIC ROCKS. General character of metamorphic rocks--Gneiss--Hornblende-schist --Mica-schist--Clay-slate--Quartzite--Chlorite-schist--Metamorphic limestone--Alphabetical list and explanation of other rocks of this family--Origin of the metamorphic strata--Their stratification is real and distinct from cleavage--Joints and slaty cleavage--Supposed causes of these structures--how far connected with crystalline action 463 CHAPTER XXXVI. METAMORPHIC ROCKS--_continued_. Strata near some intrusive masses of granite converted into rocks identical with different members of the metamorphic series--Arguments hence derived as to the nature of plutonic action--Time may enable this action to pervade denser masses--From what kinds of sedimentary rock each variety of the metamorphic class may be derived--Certain objections to the metamorphic theory considered--Lamination of trachyte and obsidian due to motion--Whether some kinds of gneiss have become schistose by a similar action 473 CHAPTER XXXVII. ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS. Age of each set of metamorphic strata twofold--Test of age by fossils and mineral character not available--Test by superposition ambiguous--Conversion of dense masses of fossiliferous strata into metamorphic rocks--Limestone and shale of Carrara--Metamorphic strata of modern periods in the Alps of Switzerland and Savoy--Why the visible crystalline strata are none of them very modern--Order of succession in metamorphic rocks--Uniformity of mineral character--Why the metamorphic strata are less calcareous than the fossiliferous 481 CHAPTER XXXVIII. MINERAL VEINS. Werner's doctrine that mineral veins were fissures filled from above--Veins of segregation--Ordinary metalliferous veins or lodes--Their frequent coincidence with faults--Proofs that they originated in fissures in solid rock--Veins shifting other veins--Polishing of their walls--Shells and pebbles in lodes--Evidence of the successive enlargement and re-opening of veins--Fournet's observations in Auvergne--Dimensions of veins--Why some alternately swell out and contract--Filling of lodes by sublimation from below--Chemical and electrical action--Relative age of the precious metals--Copper and lead veins in Ireland older than Cornish tin--Lead vein in lias, Glamorganshire--Gold in Russia--Connection of hot springs and mineral veins--Concluding remarks 488 * * * * * _Dates of the successive Editions of the "Principles" and "Elements" (or Manual) of Geology, by the Author._ Principles, 1st vol. in octavo, published in - - - Jan. 1830. ----, 2d vol. do. - - - - - - - - - - - - - - - - Jan. 1832. ----, 1st vol. 2d edition in octavo - - - - - - - 1832.