CONTENTS. 3 



Page. 

 Chapter VI. — The criteria and principles used by authors in the correlation 

 of the various parts composing the group, with observations on some methods 



of correlation 391 



Historical notes 391 



America 391 



Maclure 391 



Eaton 392 



Bigsby 395 



James 396 



Bakewell 397 



DelaBeche 398 



Eaton 399 



Conrad 399 



Hall 401 



Emmons 403 



Rogers 403 



Safford 405 



Canada 405 



Logan 405 



Newfoundland 406 



Dana 407 



Mississippi Valley 408 



Hall 408 



Winchell 409 



Meek „ 410 



Rocky Mountains 411 



Whitney 411 



Bradley 411 



Fortieth Parallel Survey 412 



Explorations and Surveys West of One Hundredth Meridian 412 



Geological Surveys of the Territories 412 



U. S. Geological Survey 413 



Correlations with European formations 414 



De Verneuil 414 



Hall 415 



Barrande 416 



Rogers 417 



Bigsby 418 



Agassiz — „ 419 



Matthew 420 



Methods of correlation 421 



Superposition 421 



Organic remains 422 



Life zones 424 



Stage of evolution 425 



Life history 426 



Contemporaneity and homotaxis 427 



Percentage of species 428 



Lithologic character 428 



Unconformity 429 



Miscellaneous 432 



Homogeny 432 



Topographic features „ 434 



