RELATION OF RADIOACTIVITY TO VULCANISM 755 



The most striking phenomenon of recent vulcanism is the pecuHar 

 distribution of volcanoes. It is well known that the great majority 

 of active volcanoes lie along two immense circles — the one encompass- 

 ing the Pacific Ocean, and the other cutting this at an angle and pass- 

 ing through the Mediterranean region, the Himalayan region, and 

 the West Indies. Many volcanoes occur outside of these two great 

 belts, but in such cases are usually related to mountain chains either 

 continental or submerged in a long line of islands, or to steep (gener- 

 ally rising) coast lines, or to long submarine plateaus or ridges. With- 

 out entering into any detailed discussion of these major volcanic lines, 

 it may be asked : Why are there so many spots of local radioactivity 

 — in other words, of peculiar chemical constitution — arranged at short 

 intervals along these lines ? A mere statement of the question shows 

 that our theory demands too special and peculiar conditions. These 

 same belts are well-known zones of seismic activity, but they are most 

 fundamentally zones of diastrophic activity, and are closely related, 

 commonly as bounding or separating tracts, to the earth's greater 

 morphological units. Judged from the crustal evidences of earth 

 movements and of the volcanic activities of the earlier periods, this rela- 

 tionship of volcanoes to critical morphological lines — belts of earth 

 movement or diastrophic activity — has held throughout recorded geo- 

 logical time. If earthquakes, lines of upheaval, or other major move- 

 ments and volcanoes are all dependent for their localization on the 

 greater diastrophic activities, this striking association and alignment 

 of them all would naturally be expected ; but if the volcanoes depend 

 for their origin on some irregular distribution of small patches of 

 radioactive matter, this association and alignment are hard to under- 

 stand. 



Another characteristic of volcanoes which is considered a strong 

 argument for a special theory of radioactivity is the repetitive nature 

 of volcanic eruptions. The melting of rock by radioactive processes 

 may easily be imagined to give rise to periodic outbursts of lava ; but, 

 even if the details of the process cannot be figured, would we not expect 

 the same periodic character if volcanoes were an expression of dia- 

 strophic activity? 



Earthquakes are commonly caused by movement along a "fault" 

 plane ; and this movement is apparently usually repetitive . The topo- 



