CONTENTS 7 



XL THE ARCHEOZOIC ERA . . . , . .317 



XII. THE PROTEROZOIC ERA 322 



PROTEROZOIC ROCKS OF THE LAKE SUPERIOR REGION . 322 



PROTEROZOIC ROCKS IN OTHER REGIONS .... 325 



GENERAL CHARACTERISTICS OF THE PROTEROZOIC GROUP 327 



LIFE IN THE PROTEROZOIC ERA 329 



QUESTIONS 330 



XIII. THE CAMBRIAN PERIOD 331 



XIV. THE ORDOVICIAN PERIOD 339 



XV. THE SILURIAN PERIOD 349 



XVI. THE DEVONIAN PERIOD 358 



DEVONIAN IN THE WEST 359 



DEVONIAN IN THE EAST 359 



MIGRATIONS AND CHANGES OF THE SEA LIFE . . . 361 



' LIFE ON LAND . . 367 



QUESTIONS 368 



XVII. THE MISSISSIPPIAN PERIOD 369 



LIFE OF THE MISSISSIPPIAN SEA ..'... 372 



QUESTIONS 375 



XVIII. THE PENNSYLVANIAN PERIOD. . . .376 



LIFE OF THE COAL SWAMPS 382 



QUESTIONS . . 387 



XIX. THE PERMIAN PERIOD 389 



SUMMARY OF THE PALEOZOIC ERA . . ... 394 



QUESTIONS 396 



XX. THE TRIASSIC PERIOD 397 



LIFE OF THE TRIASSIC 399 



QUESTIONS 404 



XXI. THE JURASSIC PERIOD .405 



LIFE OF THE JURASSIC 409 



QUESTIONS 413 



