in snow flakes 333 Plate 52.—The Devil’s Tower, Wyoming, an example of igneous rock with columnar structure, and resting on sedimentary rocks 334 Courtesy of the U. S. Geological Survey Plate 53.—A coarse granite. Graphic granite 335 Plate 54.—Syenite. Gabbro 336 Plate 55.—Basalt-porphyry. The large white crystals are phenocrysts of plagioclase feldspar. Basalt-obsidian 337 Plate 56.—Amgydoloid 338 Plate 57.—The north face of Scott’s Bluff, Neb., showing sedimentary sandstones above and clays below. The type of erosion is characteristic of arid regions 339 Courtesy of the U. S. Geological Survey Plate 58.—Breccia. Conglomerate 340 Plate 59.—Calcareous shale. Coquina 341 Plate 60.—Foramenifera from chalk; enlarged about 25 diameters. Encrinal limestone; fragments of the stems, arms and body of crinoids 342 Plate 61.—Amber. Two bottles of petroleum, the left hand one with a paraffin base, the right hand one with an asphalt base (_in color_) 308 Plate 62.—Diatomaceous earth magnified 50 times. Two diatoms from the above enlarged 250 times 343 After Gravelle, by the courtesy of Natural History Plate 63.—A metamorphic rock, showing the contortion of layers due to expansion under heat 344 Plate 64.—A conglomerate partly metamorphosed to a gneiss. A typical gneiss 345 Plate 65.—Mica schist, with garnets. Chlorite schist (_in color_) 309 Plate 66.—Phyllite. A white marble, with black streaks due to graphite 346 Plate 67.—Serpentine composed of serpentite, hematite, and some calcite (_in color_) 310 Plate 68.—Claystones, simple and compound. A lime concretion, which on splitting disclosed a fern leaf of the age of the coal measures 347 Plate 69.—A septeria from Seneca Lake, N. Y. Pisolite from Nevada 348 Plate 70.—A geode filled with quartz crystals 349 Plate 71.—A quartz pebble from the bed of a New England brook. A pebble of schist and granite from the foot of Mt. Toby, Mass. 350 Plate 72.—An iron-nickel meteorite, of 23 lbs., which fell in Claiborne Co., Tenn. An etched slice of an iron meteorite