216 ROCKS AND SOIL 



The great mass of rock below the mountain jutting out into the forest is a lava flow 

 Once it was molten lava, now it forms what kind of rock ? 



PROBLEM I. HOW WERE THE ROCKS FORMED? 



Three Ways in Which Rocks Were Formed. Let us go 



out into the field to answer this question. You will find, 

 depending upon where you happen to look, various kinds 

 of rock. Rocks of one kind appear to be made up of 

 pieces of different kinds of substance, all mixed up to- 

 gether as if a giant had stirred them all up while hot and 

 they had cooled quickly. Probably the original rocks 

 of the earth were formed as molten masses of semifluid 

 material, like lava that flows from a volcano during an 

 eruption. Such rocks are called igneous, of which granite 

 is an example. 



Others look as if they were formed in layers. Such 

 rocks, like sandstone, shale, or limestone, were actually 

 formed from particles of ground-up rock being deposited 

 under water. Layers upon layers were made ; the lower 

 layer may have been carried down miles below the surface 

 of the earth, and when subjected to heat, pressure, and 

 chemical action the particles were cemented into solid 



