PLATE 42. Rocks. 



Figure 



1. Fluid-lacunas in quartz, magnified 120 diameters. 



2. Glass-lacunas in triclinic felspar. Lava of A.D. 1607 ; near Raudazzo, Etna '> 



77 diams. Crossed Nicols. 



3. Trichites in obsidian. Yellowstone district, U. S., 250 diams. 



4. Crystallites in obsidian. Mexico, 30 diams. 



5. Microliths (belonites) of augite, in pitchstone. Corriegills, Arran, 55 diams. 



6. Spherules in obsidian. Lipari, 25 diams. 



7. Perlite. Buschbad, near Meissen, Saxony, 18 diams. 



8. Fluxion structure around sanidine crystals in obsidian. Lower Geyser basin, 



Yellowstone district, Colorado, U. S., 18 diams. 



9. Granite. Cornwall, 25 diams. Polarized light. (Orthoclase, plagioclastic fel- 



spar, quartz, and biolite.) 



10. Syenite. Hemsbach, Germany, 30 diams. Polarizer only. (Hornblende, ortho- 



clase, quartz, and magnetite.) 



11. Minette (mica trap). Seifersdorf, Saxony, 55 diams. 



12. Felstone (halleflinta). Schiesshyttan, Sweden, 120 diams. Grossed Nicols. 



13. Trachyte. Drachenfels, Rhine, 55 diams. Polarized light. (Sanidine, oligoclase 



sphene, <fec.) 



14. Phonolite. Hohgau, Germany, 33 diams. (Nosean and hornblende.) 



15. Diorite. Ontario, 55 diams. Polarized light. (Hornblende, triclinic felspar, 



apatite, &c.) 



16. Basalt. Wohlbach, near Adorf, Saxony, 18 diams. Polarized light. (Porphy- 



ritic olivine crystals and magnetite.) 



17. Basalt. Giant's Causeway, Ireland, 77 diams. Polarized light. (Olivine, tri- 



clinic felspar, magnetite.) 



18. Basalt. Titterstone, Clee Hill, Shropshire, 77 diams. Polarized light. (Augite, 



triclinic felspar, apatite, &c.) 



19. Phonolite. Wolf Rock, Cornish coast, 33 diams. (Nepheline and hornblende.) 



20. Mica schist. Braunsdorf, Saxony, 18 diams. (Biolite and quartz.) 



21. Millstone grit (coarse felspathic sandstone). Black Rocks, Cromford, Derby- 



shire, 18 diams. Polarized light. (Fragments of quartz and felspar, with 

 ferruginous cement.) 



22. Slate (Cambrian). Penrhyn Quarries, North Wales, 250 diams. Grossed 



Nicols. 



23. Great Oolite. Grimsthorpe Park, Lincolnshire, 18 diams. 



24. Carrara marble, 33 diams. Polarized light. 



The minerals mentioned, in brackets, form prominent objects in the drawings ; 

 but do not necessarily include all the constituents of the different rocks. 



