BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 30, pp. 499-566 DECEMBER 30, 1919 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



EVOLUTION OF GEOLOGIC CLIMATES^ 



BY F. H. KNOWLTO]^ 



{Read before the Paleontological Society December 28, 1918) 



CONTENTS 



Page 



Introduction 500 



Part I. Paleobotanical evidence in the interpretation of geologic climates. 501 



Temperature toleration in plants and animals 501 



Paleobotanical criteria for determination of climatic conditions 503 



Evidence of the floras 506 



Algonkian flora 506 



Cambrian and Ordovician floras 507 



Silurian floras 507 



Devonian floras 507 



Carboniferous floras 510 



In general 510 



Mississippian floras 510 



Pennsylvanian floras 511 



Permian flora and its climatic significance 514 



Triassic floras 515 ^ 



Late Triassic and early Jurassic time 516 



Jurassic floras 517 



Cretaceous floras 520 



Lower Cretaceous 520 



Upper Cretaceous 524 



Climate of Upper Cretaceous time 525 



Tertiary floras 528 



Origin of herbaceous types of vegetation 528 



Eocene floras and their probable climatic requirements 529 



Miocene floras and their climatic requirements 534 



Pliocene floras and their climatic requirements ... 536 



Part II. Origin and differentiation of geologic climate 537 



Early climates non-zonal 537 



Consideration of the atmosphere 539 



Power of clouds in reflecting the sun's rays 540 



Manuscript received by the Secretary of the Society August 23, 1919. 

 Published with the permission of the Director of the U. S. Geological Survey, 

 Entered on the printed program as "Climates of the past." 



(499) 



