CONTENTS 285 



Page 



Deductions based on jjjradational criteria 477 



Lateral cliauge in character of syuclironous deposits within the same 



basin 477 



Change not the rule 477 



The case of the Saint Peter sandstone 47!) 



Paleontological criteria 481 



General discussion 481 



Fossil faunas and floras 482 



Centers of origin and dispersal of fossil marine faunas 4&3 



Paleozoic Atlantic faunal realm and its subdivisions 483 



The three subfaunas 483 



Silurian routes of migration 485 



Gulf of Mexico invasions 486 



The Arctic center of dispersal 487 



The Pacific faunas 48t) 



Deductions based on faunal distribution 401 



Effect of expansion and restriction of continental seas on evolution. . . 405 

 Mutation of fossil marine faunas accomplished before they invaded 



continental seas 408 



Examples of localization in development of Paleozoic faunas 501 



Principles of stratigraphic correlations 505 



General discussion of the principles 505 



Correlation by means of organic remains 506 



General discussion 506 



Summary statement of principles 507 



( 1 ) Systematic paleontology 507 



(2) "Matching" of species and genera 508 



(3) Dominant species 508 



(4) True guide fossils 500 



(5) Sequence of life zones 510 



(6) Varying time values of faunal breaks 511 



(7) Barriers prohibiting intermingling of distinct faunas. .. 512 



(8) Recurrent species and faunas 513 



CO) Time range of fossil species and genera 514 



(10) Tndexical value of s])ecies in distinct provinces 514 



Ml) I'rovincial differences in introductory faunal facies.... 51(; 



(12) Value of pelagic species in correlation 517 



(13) TIelation of marine currents to faunal distribution 517 



Correlation by lithologic similarity 510 



Value of this method 510 



(1) Importance of geographic persistence of lithologic characters 



in establishing contemporaneity of deposition 520 



(2) Sandstones often of low value in correlation 521 



(3) Similarity in lithologic character and stratigraphic position 



does not establish contemporaneity 522 



(4) Correlation of dissimilar lithologic units 523 



(5) Sequence of lithologic units 525 



' (6) Apparent lithologic units often include stratigraphic hiatuses. 526 



(7) Passage beds with or without interrupted sedimentation 528 



Correlation by diastrophic movements 532 



