378 J. BARRELL RECOGJSITION OF ANCIENT DELTA DEPOSITS 



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Variegated formations 417 



Greeu shales and red sandstones 417 



Recent example, the basin of eastern I'ersia 417 



Ancient example, the Orcadie basin of Scotland 418 



Red shales and green sandstones 419 



Subrecent example, the Siwalik formations of India 419 



Ancient example, the Catskill formation 421 



Lateral and vertical variegations in clays 422 



Regular banding in mudstones 423 



A climatic record in bottomset beds 423 



Banded slates of the Orange group, by D. D. Cairnes 424 



Relations of bedding to mode of sedimentation 423 



Method of presentation 425 



Lamination of mudstones 425 



Effects of subsidence from suspension 42o 



Effects of waves 426 



Effects of subaerial actions 426 



Stratification of sandstones 427 



Effects of waves 427 



Effects of currents 430 



Contrasts of marine and fluviatile aition 432 



Effects of sheet-flood deposition 433 



Effects of wind 434 



Relations of texture to sedimentation 435 



Degree of sorting a negative criterion 435 



Effects of wind in shaping sand 435 



Combinations of wind and water action 436 



Kinds of combined structures and textures 436 



Relative association of eolian nction with fluviatile and marine 



deposits 436 



Climates implied by eolian action 438 



Desert clinuites and dominant dune structures 438 



Semi-arid climates and dominant combined structures 438 



Breadth of eolian action as a criterion of fluviatile deposits 440 



Significance of conglomerates 440 



Mud cracks and rainprints 442 



Terrestrial fossils as evidence of terrestrial deposits 443 



Free terrestrial fossils, plants and animals 443 



Fixed terrestrial fossils, plants and animals 444 



General conclusion on criteria for delta deposits 445 



Introduction 



On the earth's surface, ranging from mountain crests to oceanic deeps, 

 are wide gradations in geologic process and organic environment, but the 

 line which most sharply draws division between two worlds of process 

 and of life is the strand. In the study of the sediments, holding as they 



