Chapter 31

General Aspect of Plutonic Rocks. — Granite and its Varieties. — Decomposing into Spherical Masses. — Rude columnar Structure. — Graphic Granite. — Mutual Penetration of Crystals of Quartz and Feldspar. — Glass Cavities in Quartz of Granite. — Porphyritic, talcose, and syenitic Granite. — Schorlrock and Eurite. — Syenite. — Connection of the Granites and Syenites with the Volcanic Rocks. — Analogy in Composition of Trachyte and Granite. — Granite Veins in Glen Tilt, Cape of Good Hope, and Cornwall. — Metalliferous Veins in Strata near their Junction with Granite. — Quartz Veins. — Exposure of Plutonic Rocks at the surface due to Denudation.