io6 



REGINALD A. DALY 



portions for the two parts of the mixture. Such a mixture could 

 occur in the main volcanic vents at great depth, provided that 

 the ferromagnesian and cafemic molecules settled down from the 

 magma in the upper part of the vent, where gravitative differentia- 

 tion was taking place. 



This explanation of the ultra-femic phases is favored by the 

 consideration that no fact in the field relations opposes the assump- 

 tion of a very deep, direct source for these heavy magmas. The 

 flow of 1852 emanated from a fissure in Mauna Loa, about 1,300 

 meters below the top of the main conduit of the island; and the 

 laccolithic body exposed in the wall of Kilauea is 3,000 meters 



TABLE VII 



below the same level. In either case, the level in the conduit 

 where it was tapped to form the erupted body may have been 

 several kilometers still lower down in that conduit. 



Origin of the less femic types. — The hypothesis that the ultra- 

 femic rocks represent the products of mixture of the average basalt 

 with the ferromagnesian and cafemic substances (more specifically 

 the molecules represented in the phenocrysts of the normal basalt) 

 settled down from higher levels in the main Hawaiian vent, implies 

 that more salic and more alkalic magma is formed at those higher 

 levels. According to the thoroughness of the gravitative differen- 

 tiation, the less dense magmas would vary in the degree in which 



