[1] Keilhau, Gæa Norvegica, pp. 61-63.
[2] Geol. Manual, p. 479.
[3] Syst. of Geol., vol. i, pp. 210, 211.
[4] See Lyell, Quart. Geol. Journ., vol. i, p. 199.
[5] Phil. Trans., 1804.
[6] Daubrée, Sur le Métamorphisme. Paris, 1860.
[7] See Principles, Index, “Carbonated Springs,” etc.
CHAPTER XXXIV.
METAMORPHIC ROCKS—continued.
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.
We have already seen that chemical forces of great intensity have frequently acted upon sedimentary and fossiliferous strata long subsequently to their consolidation, and we may next inquire whether the component minerals of the altered rocks usually arrange themselves in planes parallel to the original planes of stratification, or whether, after crystallisation, they more commonly take up a different position.