xvm CONTENTS. 



' PAGE 



Protozoa, 287. Unidentified forms, 288. Implied life, 288. 

 Sociological development, 291. Mental development, 291. 

 Ecological adaptations, 292. Zoological provinces, 292. 

 Comparison of pre-Cambrian and post-Cambrian evolution, 

 293. 



The Succession of Faunas 294 



The Lower Cambrian or Olenellus fauna, 296. The 

 Middle Cambrian or Paradoxides fauna, 298. The Upper 

 Cambrian or Dikellocephalus fauna, 299. The foreign Cam- 

 brian faunas, 299. The abrupt appearance of the Cambrian 

 fauna, 301. Brooks' hypothesis, 301. A second hypothesis, 

 302. 



CHAPTER VI. 



THE ORDOVICIAN (LOWER SILURIAN) PERIOD. 



Formations and Physical History. ' . . . . . 304 



Sedimentiaton during the Ordovician Period: 304 



Sections of the Ordovician. 309 



New York section, 309. Upper Mississippi section, 

 313. The Appalachian sections, 315. Section in New 

 Jersey, 318. Section in western Maryland, 318. Sec- 

 tion in eastern Kentucky, 319. Sections in the interior, 

 319. Section in southeastern Minnesota, 320. Section 

 in central Texas, 320. General conditions in the eastern 

 part of the continent, 321. Western sections, 322. 



Igneous Rocks 322 



General Conditions and Relations of the Ordovician System. . . . 322 

 Position of beds, 322. Present condition of the for- 

 mations, 324. Exposure of the Ordovician rocks, 326. 

 Thickness, 330. Width and position of outcrops, 331. 



Close of the Ordovician Period 332 



Economic Products ....:". 336 



t ■. , . Foreign Ordovician. 338 



Ordovician Life 342 



i, Close sequence upon the Cambrian, 342. ' 



Edaphic, Provincial, and Cosmopolitan Development. .'. ': ... 343 



(: , ' . . , (1) Edaphic modifications, 343. (2) Provincial modifica- 

 tions, 343. (3) Cosmopolitan development, 344. 

 The General Progress of Ordovician Life. . - - 346 



