CONTENTS 15 



CHAPTER XVI 

 THE ORDOVICIAN PERIOD 



PAGE 



Ordovician Physical Geography 418 



Close of the Ordovician. Cincinnati Anticline. Volcanism. Ordovician 

 of Other Continents. 

 Petroleum and Natural Gas 424 



Conditions Favoring the Accumulation of Oil and Gas. Origin of Oil and 

 Gas. Life of Oil Wells and Fields. 

 Life of the Ordovician 427 



Protozoa. 



Cozlenterata: Sponges. Graptolites. Stromatopora. Corals. 



Echinodermata : Cystoids. Crinoids. Blastoids, Starfish, Brittle Stars, and 

 Sea Urchins. 



Molluscoidea: Brachiopods. Bryozoa. 



Mollusca: Pelecypods. Gastropods. Cephalopods. 



Crustacea: Trilobites. Other Arthropods. 



Fishes. 

 Plants 436 



Seaweeds. 

 Summary 436 



Progress and Character of Ordovician Life. Climate and Duration of the 

 Ordovician. 



CHAPTER XVII 

 THE SILURIAN PERIOD 



Silurian Physical Geography ■ . 439 



Geography of the Silurian. Character and Thickness of the Sediments. 

 Clinton Iron Ore. Deserts. Origin of Rock Salt. Igneous Rocks. 

 Other Continents. 



Life of the Silurian 444 



Ccelenterata: Corals. Other Coelenterates. 

 Echinodermata: Crinoids. Cystoids. 

 Molluscoidea: Brachiopods. Bryozoa. 

 Mollusca: Gastropods. Pelecypods. Cephalopods. 

 Arthropoda: Trilobites. Eurypterids. Scorpions. 

 Fishes. 



Summary 450 



Life on the Land. Migration. Climate and Duration. Close of the Silurian. 



CHAPTER XVIII 

 THE DEVONIAN PERIOD 



Devonian Physical Geography 452 



Subdivisions of the Devonian. Geography. The Devonian in New York. 

 Continent of Appalachia. Igneous Rocks. Devonian Oil and Gas. 

 Devonian of Other Continents. 



Life of the Devonian 456 



Ccelenterata: Corals. 



cleland geol. — 2 



