CONTENTS. xix 



PAGE 



The scantiness of the record of land life, 346. The first 

 record of insect life, 346. The mian record marine, 347. 

 The appearance of the vertebrates, 347. The climax of the 

 trilobites, 347. Other crustaceans, 351. The dominance of 

 the cephalopods, 352. The gastropods, 354. The pelecy- 

 pods, 354. The abundant development of the brachiopods, 

 355. The abundance of the bryozoans, 357. The deploy- 

 ment of the echinoderms, 357. The development of the 

 ccelenterates, 360. Other forms, 361. Implied life, 361. 

 Ecological, social, and mental development, 363. 



The Succession of Faunas 364 



1. The fauna of the Calciferous, 364. 2. The Chazy 

 fauna, 365. 3. The Mid-Ordovician fauna, 365. 4. The 

 Upper Ordovician fauna, 367. 



The Ordovician Faunas of Other Continents 367 



CHAPTER VII. 



THE SILURIAN (UPPER SILURIAN) PERIOD. 



Formations and Physical History 368 



Subdivisions of the Silurian System = 370 



The Oswegan Series . 371 



The Oneida formation, 371. The Medina formation, 373. 

 The Niagaran Series 375 



The Clinton formation, 375. The Niagara formation, 377. 



The Salina (Cayugan) Series. . . 386 



The Salina series, 386. Associated formations, 389. 



Silurian in the West 390 



The Helderberg Formation 391 



Summary 391 



Outcrops 392 



Former Extent and General Stratigraphy 392 



Igneous Rocks 394 



Close of the Silurian 395 



Foreign Silurian 395 



Climate 396 



The Silurian Life. 



The Transition from the Ordovician 397 



The Expansional Stage and the Mid-Silurian Fauna 399 



