258 SCIENCE SKETCHES. 



undisturbed by the fires within, and were clear 

 and cold as mountain brooks should be; but the 

 rain and melted snow will never all remain on the 

 surface. Some of it falls into cracks or joints or 

 porous places in the rock, and from this come 

 underground streams or springs. But in this 

 region a stream could not run long underground 

 without coming in contact with the old still-burning 

 fires. When a crust is formed over the lava, it 

 cools very slowly. When the crust is a rod or 

 two deep, the lava within is almost as well pro- 

 tected as if it were at the centre of the earth. 



Whenever the water came down into the fire, 

 the hot rocks would be furious with indignation, 

 and tearing the water to atoms they would throw 

 it back to the surface as steam. Then the ex- 

 plosive force of the steam would in turn tear up 

 the rocks, making still larger the hole through 

 which the water came. When the rocks were 

 very hot, a little water upon them would make a 

 terrible commotion like the shock of an earth- 

 quake. When much water came down, it would 

 hiss and boil high in the air, as it tried to break 

 the cushion of steam which came between it and 

 the lava. 



And all this went on in hundreds of places and 

 maybe for thousands of years. The hot rocks 

 glowed and sweltered in the ground, and the cold 

 snow-water crept after them closer and closer, 

 while more and more vigorously the rocks re- 

 sented the intrusion. Sometimes the water would 

 go down in a mass through a cleft, when it would 

 be hurled back bodily the very way it came. At 



