BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 27, PP. 345-386 JUNE 5, 1916 



DOMTNANTLY PLUVIATILE ORIGIN UNDER SEASONAL 

 RAINFALL OP THE OLD RED SANDSTONE 1 



BY JOSEPH BARRELL 



(Presented before the Society December 28, 1915) 



CONTENTS 



Introduction 345 



Prevailing views regarding conditions of origin 349 



Criteria as to modes of origin of sediments 352 



Description of the Old Red Sandstone formations 362 



General relations 362 



Uppermost Silurian — Downtonian formations 364 



Lower Devonian — Lower Old Red 366 



Middle Old Red — Orcadian formations 370 



Relations to older rocks 370 



Old Red of the Moray Firth. 371 



Formations of the Orcadie basin in Caithness 371 



Old Red Sandstone of the Orkney Islands 374 



Interpretation of the Orcadian deposits 375 



Significance of conglomerates 375 



Significance of colors 376 



Significance of mud-cracks and rain-prints 377 



Significance of intercalated limestones 377 



Lowest Upper Old Red of the Shetland Islands 378 



The Upper Old Red Sandstones 379 



Geography of the British Isles in Devonian time. . 382 



General conclusions on Devonian climate in British Isles. . . 385 



Introduction 



The Devonian system is represented in the British Isles, except in the 

 extreme south of England, by a thick series of red sandstones, shales, and 

 conglomerates. Red sandstone is the predominate outcropping rock, the 

 colors of which range from light red to deep chocolate brown, but in 

 places exhibit green, yellow, gray, and mottled tints. The series of for- 



1 Manuscript received by the Secretary of the Society January 25, 1916. 



(345) 



