Note 25 — Chapter VI · PLUTONIC AND METAMORPHIC ROCKS:—CLEAVAGE AND FOLIATION.
Reading edition
Humboldt (“Personal Narrative,” vol. iv, p. 60) has described with much surprise, concretionary balls, with concentric divisions, composed of partially vitreous feldspar, hornblende, and garnets, included within great veins of gneiss, which cut across the mica-slate near Venezuela.