AN ANCIENT BEACH AT EBB TIDE 138 THE LIME ROCKS 147 THE AGE OF FISHES 152 KING COAL 155 HOW COAL WAS MADE 160 THE MOST USEFUL METAL 167 THE AGE OF REPTILES 175 THE AGE OF MAMMALS 180 THE HORSE AND HIS ANCESTORS 186 THE AGE OF MAN 194 _PART II. THE SKY_ EVERY FAMILY A "STAR CLUB" 201 THE DIPPERS AND THE POLE STAR 207 CONSTELLATIONS YOU CAN ALWAYS SEE 213 WINTER CONSTELLATIONS 219 ORION, HIS DOGS, AND THE BULL 223 SEVEN FAMOUS CONSTELLATIONS 231 THE TWENTY BRIGHTEST STARS 239 HOW TO LEARN MORE 241 ILLUSTRATIONS Pike's Peak _Frontispiece_ FACING PAGE Sand Dunes in Arizona 44 Grand Cañon of the Colorado 45 Castles Carved by Rain and Wind 52 Where All the Water Comes From 53 The Richest Gold and Silver Mines 72 Rocks Being Ground to Flour 73 A Pond Made by a Glacier 88 The Struggle Between a Stream and Its Banks 89 Ripple Marks and Glacial Striæ 102 Glacial Grooves and Markings 103 Crinoid and Ammonite 140 Fossil Corals, Coquina, Hippurite Limestone 141 Fossil Fish 152 Meteorite 153 Eocene Fish and Trilobite 156 How Coal Was Made 157 Banded Sandstone. Opalized Wood 176 Allosaurus 177 A Three-horned Dinosaur 178 Remains of Brontosaurus 179