xii CONTENTS 



THE LIFE OF THE CAMBRIAN 494 



Plant fossils, 495. Animal fossils, 495. Zoological provinces, 

 503. The succession of faunas, 504. The abrupt appearance of 

 the Cambrian fauna, 505. 



CHAPTER XVII 



THE ORDOVICIAN (LOWER SILURIAN) PERIOD 



FORMATIONS AND PHYSICAL HISTORY 507 



Sedimentation during the Ordovician period, 507. Sections of the 

 Ordivician, 509. General conditions in the eastern part of the 

 continent, 510. Igneous rocks, 513. General conditions and 

 relations of the Ordovician system, 513. Close of period, 515. 

 Economic products, 517. Foreign Ordovician, 517. Duration 

 and climate, 520. 



LIFE 521 



Edaphic adaptations, 522. Provincial modifications, 522. Cos- 

 mopolitan development, 522. Marine life, 523. Land life, 

 534. 



CHAPTER XVIII 



THE SILURIAN (UPPER SILURIAN) PERIOD 



FORMATIONS AND PHYSICAL HSITORY 536 



Silurian of the East, 537. Silurian of the West, 543. Summary, 

 544. Foreign Silurian, 546. 



SILURIAN LIFE 546 



The transition from the Ordovician, 547. The expansional stage 

 of the Mid-Silurian fauna, 547. Foreign faunas and migrations, 

 554. The closing restrictional stage, 555. 



CHAPTER XIX 



THE DEVONIAN PERIOD 



FORMATIONS AND PHYSICAL HISTORY 559 



Devonian of the East, 561. Devonian of the West, 567. Areas 

 where the Devonian cames to the surface, 569. Close of the De- 

 vonian, 571. Economic products, 570. Foreign Devonian, 571. 

 Climatic conditions, 574. 



DEVONIAN LIFE ~>7 ' 



The marine faunas, 574. Helderberg fauna, 575. Oriskany 

 fauna, 577. Onondaga fauna, 578. Southern Hamilton fauna, 

 582. Northwestern Hamilton fauna, 585. Evidence of geo- 

 graphic connections, 586. Later Devonian (Chemung) fauna, 

 586. Devonian fauna in the Great Basin area, 587. Life of 

 land waters, 588. Land life, 592. 



