The Mighty Deep 



of the earth-crust and about the rocks of which 

 it is made. 



By that word ''rock" must be understood, not 

 only such hard kinds as granite and marble, but 

 softer materials, such as chalks, clays, sands, and 

 even muds. 



Rocks generally have been roughly divided 

 into two classes — the Stratified and the Un- 

 stratified. 



Stratified Rocks, known also as Sedimentary, 

 have been put together in the past, grain by 

 grain, layer by layer, under water, built gradually 

 through ages, and slowly welded into firmness. 



Unstratified Rocks, known also as Igneous, 

 from the Latin word for "fire," have been melted 

 down by great heat into a liquid state, and have 

 then cooled into solid crystallized masses. 



When these fire-made rocks have been heaved 

 up from lower depths and are exposed to the 

 wearing effects of rain and wind, rivers and 

 waves, they too have to part with much of their 

 material, like stratified rocks, only more slowly, 

 owing to their harder make. These materials are 

 carried seaward, to be used in the building of 

 fresh stratified rocks. Then again, some kinds 

 of stratified rocks, when exposed to intense heat, 

 will crystallize into igneous rocks. So the one 



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