Part 17 (2/2)

EXPLANATION OF PLATE III.

MAGNIFIED SECTIONS OF VOLCANIC ROCKS.

1. Diorite d.y.k.e, traversing a.s.synt limestone, North Highlands.

2. Basalt from upper beds, near Giant's Causeway, County Antrim.

3. Hornblende-hypersthene-augite Andesite, from Pichupichu, Andes.

4. Augite-Andesite from Pichupichu, Andes.

5. Olivine dolerite, with hornblende and biot.i.te, Madagascar.

6. Leucite basalt, with mellilite, Capo di Bove, Italy.

[Ill.u.s.tration: Plate IV.]

EXPLANATION OF PLATE IV.

MAGNIFIED SECTIONS OF VOLCANIC ROCKS.

1. Vesuvian lava, gla.s.s paste with numerous crystals of leucite; others of augite and nepheline porphyritically developed; also small grains of magnet.i.te.

2. Vesuvian lava, gla.s.s paste with numerous crystals of leucite; others of olivine, hornblende, and sanidine, porphyritically developed; small grains of magnet.i.te.

3. Trachyte from Hungary; felsitic paste with crystals of hornblende and sanidine, and a little magnet.i.te.

4. Gabbro, from Carlingford Hill, Ireland, consisting of anorthite, augite, a little olivine, and magnet.i.te.

5. Dolerite, from old volcanic neck, Scalot Hill, near Lame, consisting of labradorite, augite, olivine, and magnet.i.te.

6. Dolerite, Ballintoy, County Antrim, showing ophetic structure, consisting of augite, labradorite, and magnet.i.te.

[1] Mr. S. Allport has discovered this in the rock called the ”Wolf Rock” off the coast of Cornwall. The most important work on basalt is that by F. Zirkel, _Unters. uber mikros. Zusammensetzung und Structur der Basaltgesteine_. Bonn (1870).

[2] Zirkel, _Die mikroskopische Beschaffenheit der Mineralien und Gesteine_, p. 153. Leipsig (1873).

[3] Zirkel, _Petrog._, i. 578; B. von Cotta, p. 178 (Eng. Trans.).

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