JRJELATION OF RADIOACTIVITY TO VULCAN ISM 757 



are successive eruptions to be brought about ? We cannot reason- 

 ably imagine a solid mass of highly radioactive material melting a shell 

 of rock about it and continually erupting that shell, the core remaining 

 intact. We cannot reasonably imagine a great vessel with walls of a 

 highly radioactive material melting its contents and erupting that, 

 the walls remaining practically intact. The radioactive material 

 must be largely scattered through the mass, and must therefore be in 

 part erupted during the volcanic action. But is there enough radium 

 or like material in lavas to melt them, if they were placed at a moder- 

 ate distance beneath the surface, even taking the normal rise and 

 surrounding active rocks into consideration ? Apparently not. Have 

 any large masses of pitchblende, or other possible especially radioac- 

 tive material, ever been observed thrown out during volcanic erup- 

 tions ? On the theory of local radioactivity they should be common. 



It is well known that the basic lavas are highly heated when 

 erupted. Granites are probably molten and active under hydrothermal 

 conditions at a few hundred degrees Celsius; their structures and 

 metamorphic effects demand but a moderately high temperature, 

 possibly the least of any of the igneous rocks. Basalts flowing out on 

 the surface require 1,000° or 1200° C, and are often at a higher tem- 

 perature. But the remarkable fact is that basalts show the lowest 

 radium content of any igneous rocks examined, while granites show 

 the highest. 



It is the writer's opinion that, while radioactivity may possibly 

 explain a large part, perhaps all, of the present interior heat of the 

 earth, it is iacompetent to explain the special phenomena of volcanoes, 

 although as an important general source of heat it may supply its share 

 of the heat which figures in volcanic action. 



It may some time be shown that certain peculiarities of some vol- 

 canoes as compared with others may be due to varying local radio- 

 activity, but it would not seem that the characteristics of volcanic 

 regions as compared with non-volcanic regions could be so explained. 

 It appears that volcanoes must be looked upon as one type of 

 results of the major normal diastrophic processes developed along the 

 earth's critical mechanical Hnes, and that each volcano is not 

 dependent for its general activity upon the special chemical composition 

 of the crust immediately below its locus of eruption. 



