Difficulty of ascertaining the Age of metamorphic Strata.
Metamorphic Strata of Eocene date in the Alps of Switzerland and Savoy.
Limestone and Shale of Carrara.
Metamorphic Strata of older date than the Silurian and Cambrian Rocks.
Order of Succession in metamorphic Rocks.
Uniformity of mineral Character.
Supposed Azoic Period.
Connection between the Absence of Organic Remains and the Scarcity of calcareous
Matter in metamorphic Rocks.


CHAPTER XXXVI.

MINERAL VEINS.

Different Kinds of mineral Veins.
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 or "Slicken sides."
Shells and Pebbles in Lodes.
Evidence of the successive Enlargement and Reopening of veins.
Examples in Cornwall and in Auvergne.
Dimensions of Veins.
Why some alternately swell out and contract.
Filling of Lodes by Sublimation from below.
Supposed relative Age of the precious Metals.
Copper and lead Veins in Ireland older than Cornish Tin.