Part 5 (2/2)

Strata near some intrusive ma.s.ses 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 ma.s.ses--From what kinds of sedimentary rock each variety of the metamorphic cla.s.s 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 x.x.xVII.

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 ma.s.ses 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 x.x.xVIII.

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 s.h.i.+fting other veins--Polis.h.i.+ng of their walls--Sh.e.l.ls 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, Glamorgans.h.i.+re--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.

----, 2d vol. 2d edition do. - - - - - - - - - - Jan. 1833.

----, 3d vol. 1st edition do. - - - - - - - - - - May 1833.

----, New edition (called the 3d) of the whole work in 4 vols.

12mo. - - - - - - - - - - - - - - - - - - - May 1834.

----, 4th edition, 4 vols. 12mo. - - - - - - - - - June 1835.

----, 5th edition, do. do. - - - - - - - - - - - - Mar. 1837.

Elements, 1st edition in one vol. - - - - - - - - July 1838.

Principles, 6th edition, 3 vols. 12mo. - - - - - - June 1840.

Elements, 2d edition in 2 vols. 12mo. - - - - - - July 1841.

Principles, 7th edition in one vol. 8vo. - - - - - Feb. 1847.

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