XII • ILLUSTRATIONS. 



Page. 



Plate XLII. Fissile lithoidal rhyolite, Obsidian Cliff 364 



XLIII. Lithophysse 364 



XLIV. Columnar rhyolite 364 



XLV. Columnar Cliff, Madison Canyon 368 



XLVI. Banded perlite 370 



XLVII. Perlite with, sphernlites - 370 



XLVIII. Natural Bridge 386 



XLIX. Natural Bridge, vertical plates 386 



L. Photomicrographs of rhyolitic glasses 406 



LI. Photomicrographs of rhyolitic glasses 406 



LII. Sphernlites 410 



LIII. Sphernlites and feldspar needles 414 



LIV. Photomicrographs of micrographic phenocrysts and sphernlites 414 



LV. Photomicrographs of spherulitic structures -. 414 



LVI. Photomicrographs of spherulitic structures and feldspar microlites 422 



LVII. Diagrams of lithophys;e 422 



LVIII. Columnar structure 436 



LIX. Photomicrographs of basalt 436 



LX-LXV. Cambrian fossils 468-478 



LXVI-LXX1. Devonian and Carboniferous fossils 580-598 



LXXII-LXXVI. Mesozoie fossils 642-650 



LXXVII-CXXI. Fossil flora 794-882 



Fig. 1. Diagram showing variation in silica percentages of rocks from Electric Peak 117 



2. Diagram showing molecular variation of the rocks at Electric Peak 119 



3. Diagram showing molecular variation of the rocks of Sepulchre Mountain 136 



4. Sections of sphernlites with projecting prisms of orthoclase and a crescent-shaped belt 



free from granulation 413 



