Chapter 34

Definition of slaty Cleavage and Joints. — Supposed Causes of these Structures. — Crystalline Theory of Cleavage. — Mechanical Theory of Cleavage. — Condensation and Elongation of slate Rocks by lateral Pressure. — Lamination of some volcanic Rocks due to Motion. — Whether the Foliation of the crystalline Schists be usually parallel with the original Planes of Stratification. — Examples in Norway and Scotland. — Causes of Irregularity in the Planes of Foliation.