CHAPTER XV 
CHANGES IN THE STRATIFIED ROCKS 
Consolidation of Rocks. —The sediments of the ocean 
are mostly deposited in loose, unconsolidated condition. 
Being formed one layer upon another, in the course 
of time many of the sedimentary rocks become buried 
beneath other strata to a depth of hundreds and even 
thousands of feet. Under the pressure of this load, 
some of the finer layers become compacted into a solid 
rock. 
Usually this pressure has been accompanied by 
another and more potent cause of consolidation ; 
namely, the deposit of some substances from solution, 
by means of which the fragments are cemented to- 
gether. Even at the surface this cementing process 
may sometimes be seen. 
Percolating water bearing in solution salts of iron 
or carbonate of lime, often transforms a gravel bed 
to solid rock by depositing a cement of the dissolved 
substances. Also, on coral islands, the hills of coral 
sand are sometimes made into rock by the action of 
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