The Interior of the Earth 



one region. This might explain the independ- 

 ence of the paroxysms and the difference of the 

 products of neighbouring volcanoes. The Italian 

 volcanoes, though very close together, act 

 usually as if thousands of miles apart. There 

 is, as a rule, no correspondence between their 

 eruptive periods, and the lavas emitted are far 

 from identical in chemical composition, as might 

 be expected if they communicated with adjoin- 

 ing points of the same internal mass. Similarly 

 no relation has been discovered between the 

 periods of activity of the two volcanoes on 

 Hawaii, whose craters are only twenty miles 

 apart. 



Let us, however, examine the facts more 

 closely. First of all, if the independence of 

 volcanoes is the rule it is not a rule without 

 exceptions. In 1865 Etna, Vesuvius and Strom- 

 boli were in simultaneous activity, and eruptions 

 occurred a few months later, in January 1866, at 

 Santorin in the Cyclades. Similar coincidences 

 have been observed frequently enough with 

 regard to the Central American volcanoes. At 

 the present it is difficult not to attribute to a 

 single cause the recent earthquakes in Calabria, 



us 



