206 LIGHT SCIENCE FOR LEISURE HOURS. 



hundred- weight, that had been thrown out by the 

 crater, lay near the source of the current of lava. I 

 raised it up on one end, and then let it fall in upon 

 the liquid lava, when it gradually sank beneath the 

 surface and disappeared. If I wished to describe the 

 manner in which it acted upon the lava, I should say 

 that it was like a loaf of bread thrown into a bowl 

 of very thick honey, which gradually involves itself 

 in the heavy liquid, and then slowly sinks to the 

 bottom." 



But, as the lava flowed down the mountain-slopes, 

 it lost its brilliant whiteness ; a crust began to form 

 upon the surface of the still molten lava, and this 

 crust broke into innumerable fragments of porous 

 matter, called scoriae. Underneath this crust across 

 which Dr. Clarke and his companions were able to 

 pass without other injury than the singeing of their 

 boots the liquid lava still continued to force its way 

 onward and downward past all obstacles. On its 

 arrival at the bottom of the mountain, says Dr. Clarke, 

 " the whole current," encumbered with huge masses of 

 scoriae, " resembled nothing so much as a heap of 

 unconnected cinders from an iron-foundery," " rolling 

 slowly along," he says in another place, " and falling 

 with a rattling noise over one another." 



After the eruption described by Dr. Clarke, the 

 great crater gradually filled up. Lava boiled up from 

 below, and small craters, which formed themselves 



