Note 31 — Chapter VI · PLUTONIC AND METAMORPHIC ROCKS:—CLEAVAGE AND FOLIATION.

I have seen in Brazil and Chile concretions thus enfolded by foliated gneiss; and Macculloch (“Highlands,” vol. i, p. 64) has described a similar case. For analogous cases in clay-slate, see Professor Henslow’s Memoir in “Cambridge Phil. Trans.,” vol. i, p. 379, and Macculloch’s “Class. of Rocks,” p. 351. With respect to both foliation and cleavage becoming tortuous where quartz-veins abound, I have seen instances near Monte Video, at Concepcion, and in the Chonos Islands. See also Mr. Greenough’s “Critical Examination,” p. 78.