SOILS 



283 



FIG. 242. Limestone, Logan County, 

 Ohio. 



of sand cemented together, 

 while limestone is made 

 from the remains of dead 

 sea animals (Figure 242). 

 Metamorphic rocks are 

 modified forms of either 

 igneous or sedimentary 

 rocks. Heat and pressure 

 are the agents which pro- 

 duce these changes (Fig- 

 ure 243). 



The surface of the earth differs from place to place due 

 to the variety of positions in which these rocks are placed. 



In some regions the 

 surface is folded into 

 mountains, in other 

 regions there are deep 

 basins filled with the 

 water of the oceans. 



Weathering. - 

 The changes in the 

 earth's surface which 

 are due to atmos- 

 pheric conditions are 

 called weathering. 

 Rocks which are ex- 

 posed to the atmos- 

 phere are gradually 

 decomposed. The 

 rate of the decompo- 

 sition depends upon 

 the climate. If the 



FIG. 243. Metamorphic Rock. . . 



Granite quarries, Concord, N. H. climate IS moist and 



