1. Vesicular structure, Lava from Ascension Island, slightly less than natural size 15 2. Elongation and branching of steam-vesicles in a lava, Kilninian, Isle of Mull, a little less than natural size 17 3. Microlites of the Pitchstone of Arran (magnified 70 diameters) 19 4. Perlitic structure in Felsitic Glass, Isle of Mull (magnified) 19 5. Spherulitic structure (magnified) 19 6. Micropegmatitic or Granophyric structure in Granophyre, Mull (magnified) 20 7. Ophitic structure in Dolerite, Gortacloghan, Co. Derry (magnified) 20 8. Variolitic or orbicular structure, Napoleonite, Corsica (nat. size) 22 9. Flow-structure in Rhyolite, Antrim, slightly reduced 23 10. Lumpy, irregular trachytic lava-streams (Carboniferous), East Linton, Haddingtonshire 24 11. View at the entrance of the Svinofjord, Faroe Islands, illustrating the terraced forms assumed by basic lavas 25 12. Sack-like or pillow-form structure of basic lavas (Lower Silurian), Bennan Head, Ballantrae, Ayrshire 26 13. Alternations of coarser and finer Tuff 34 14. Alternations of Tuff with non-volcanic sediment 35 15. Ejected block of basalt which has fallen among Carboniferous shales and limestones, shore, Pettycur, Fife 37 16. Effects of denudation on a Vesuvian cone 40 17. Section to illustrate the structure of the Plateau type 43 18. Diagram illustrating the structure and denudation of Puys 45 19. Section illustrating submarine eruptions; alternations of lavas and tuffs with limestones and shales full of marine organisms 48 20. Diagram illustrating volcanic eruptions on a river-plain 49 21. Diagram illustrating volcanic eruptions on a land-surface 50 22. Ground-plans of some volcanic vents from the Carboniferous districts of Scotland 55 23. View of an old volcanic "Neck" (The Knock, Largs, Ayrshire, a vent of Lower Carboniferous age) 56 24. Section of neck of agglomerate, rising through sandstones and shales 58 25. Neck filled with stratified tuff 64 26. Section of neck of agglomerate with plug of lava 65 27. Section of agglomerate neck with dykes and veins 66