BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 33, PP. 765-804 NOVEMBER 2. 1922 



DECCAN TRAPS AND OTHER PLATEAU BASALTS 1 



BY H. S. WASHINGTON 



(Bead before the Society December SO, 1921) 



CONTENTS 



Page 



Introduction 765 



The Deccan traps 766 



The Oregonian region 775 



Thulean basalts 780 



General discussion 780 



Iceland 781 



Faroe Islands 785 



Other Thulean basalts 787 



Siberian basalts 791 



Patagonian basalts 793 



Algonkian and Palisadan regions 795 



Conclusions 797 



Characters of plateau basalts 797 



Classification of basalts 800 



Cause of fluidity 803 



Introduction 



In various parts of the earth and at different geological horizons are 

 large areas covered by very extensive, generally horizontal, series of sheets 

 of basaltic lavas, the series of overlying flows often attaining thicknesses 

 of thousands of meters. In some cases they are accompanied by flows of 

 rhyolite. These basalts have poured out in an evidently very fluid con- 

 dition, as they occupy preexisting valleys and cover the lower topographic 

 features much like floods of water, the separate flows being very long — 

 many of them measured by miles. 



It is generally assumed by volcanologists that these extensive, hori- 

 zontal, very fluid flows have issued quietly from fissures — an idea first 

 suggested by Sir Archibald Geikie. 2 Volcanic cones, formed of lavas, 

 ashes, or both, are present in places, but these are inconspicuous, being 



1 Manuscript received by the Secretary of the Society April 28, 1922. 



2 Geikie : Nature, November 4, 1880. 



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