4 8 



ELEMENTARY SCIENCE 



a good deal to go on, so that we feel fairly certain of the 

 following things: 



i. That the earth, as a whole, is solid, and the deeper 

 you go the more solid it gets. The pressure increases and 



FIG. 1 8. Photograph of limestone cave, showing rock 

 icicles (stalactites). 



becomes so tremendous that the real inside of the earth is 

 as firm as steel. 



2. Yet some underground regions are fluid. They are 

 also very hot. Volcanoes prove this (see Fig. ! 9 ). The 



