Studies for Students 



RELATIVE GEOLOGICAL IMPORTANCE OF CONTINEN- 

 TAL LITTORAL, AND MARINE SEDIMENTATION 



JOSEPH BARRELL 



Yale University, New Haven, Conn. 



PART III. MUD-CRACKS AS A CRITERION OF CONTINENTAL 

 SEDIMENTATION 



Introduction 524 



Methods of Origin of Mud Cracks 526 



Conditions for Temporary Preserval 528 



Mud-Cracks of Playas 533 



Description of Present Conditions 533 



Nature of the Geological Record 535 



Mud-Cracks Marginal to Interior Lakes 537 



Description of Present Conditions . -537 



Nature of the Geological Record 537 



Mud-Cracks of River Flood Plains 538 



Description of Present Conditions 538 



Nature of the Geological Record 540 



Mud-Cracks of the Littoral Zone 543 



Discussion as to Present Origin 543 



Nature of the Geological Record '. .547 



Conclusions on Geological Significance of Mud-Cracks . . . . . 550 



Prevailing Interpretations 550 



Illustrative Geological Applications 553 



Mud-cracked formations of the pre-Cambrian 553 



Pre-Cambrian Formations of Montana 553 



The Grand Canyon Series of Arizona 560 



Conclusion on Nature of pre-Cambrian Sedimentation 566 



INTRODUCTION 



The previous parts on the relative geological importance of conti- 

 nental, littoral, and marine sedimentation have shown that the bulk 

 of present sedimentary deposits are formed either upon the land or 

 beneath the sea, and that the httoral, restricted to its distinctive 



524 



