m the lava of 1858. Mag., 40
diams.

" 11, 12, 13. Sections of plagioclase crystals (probably
labradorite) from the lava of 1855. Mag., 100 diams.

" 14. Section of olivine crystal from the lava of 1631--imperfectly
formed. Mag., 30 diams.

" 15. Section of mica-flake from the lava of 1822. Mag., 30 diams.

[Illustration: Plate III.]

EXPLANATION OF PLATE III.

MAGNIFIED SECTIONS OF VOLCANIC ROCKS.

1. Diorite dyke, traversing Assynt 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 biotite, Madagascar.

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

[Illustration: Plate IV.]

EXPLANATION OF PLATE IV.

MAGNIFIED SECTIONS OF VOLCANIC ROCKS.

1. Vesuvian lava, glass paste with numerous crystals of leucite;
others of augite and nepheline porphyritically developed; also
small grains of magnetite.

2. Vesuvian lava, glass paste with numerous crystals of leucite;
others of olivine, hornblende, and sanidine, porphyritically
developed; small grains of magnetite.

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

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

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

6. Dolerite, Ballintoy, County Antrim, showing ophetic structure,
consisting of augite, labradorite, and magnetite.

[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. ueber 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.).

INDEX.

INDEX.

Abyssinian table-lands, 190 _et seq._

Albano, Lake, 89

America, volcanic regions of North, 136 _et seq._;
of Western, 144

Andes, 18, 27, 227, 254

Andesit