72 SECRETS OF EARTH AND SEA 



to explain how the molten basalt has come to take this 

 columnar structure on cooling. It has nothing to do with 

 " crystallization," but is similar to the columnar formation 

 shown by commercial " starch " and occasionally by 

 "tabular flint." A theoretical explanation of its forma- 

 tion has been given by Prof. J. Thompson, brother of the 

 late Lord Kelvin. 



The varieties of volcanoes and their products make 

 up a long story too long to be told here. There are 

 from 300 to 400 active craters in existence to-day 

 mostly not isolated, but grouped along certain great 

 lines, as, for instance, along the Andean chain, or in 

 more irregular tracks. If we add to the list craters no 

 longer active, but still recognizable, we must multiply 

 it by ten. Vesuvius is the only active volcano on the 

 mainland of Europe Hecla, Etna, Stromboli, Volcano, 

 and the volcanoes of the Santorin group are on islands. 

 The biggest volcanoes are in South America, Mexico, Java, 

 and Japan. Volcanoes and the related " earthquakes " 

 have been most carefully studied with a view to the 

 safety of the population in Japan. The graceful and 

 well-beloved volcano, Fujiyama, is more than 12,000 ft. 

 high, but, unlike others in those islands, it has been 

 quiescent now for just 200 years. The most violent 

 volcanic eruptions of recent times, with the largest 

 "output" of solid matter, are those of the Suffriere of 

 St. Vincent in 1812, of the Mont Pel^e of Martinique in 

 1902, and of Krakatoa in 1883. A single moderate 

 eruption of the great volcano Mauna Loa, in Hawaii, 

 nearly 14,000 feet high, throws out a greater quantity 

 of solid matter than Vesuvius has ejected in all the 

 years which have elapsed since the destruction of Pompeii. 

 Many hundred millions of tons of solid matter were 

 ejected by Mont Pele'e in 1902, when also a peculiar 

 heavy cloud descended from the mountain, hot and 



