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GEOLOGY. 



A DESCRIPTION of the Structure of the Globe, 

 of the relative Situations of Rocks and Mine- 

 rals, of their Connexion with each other, and 

 of the Changes which they are undergoing, 

 and have undergone.* 



Rocks. 



A geological arrangement of rocks is founded on 

 the great relations which they bear to each other, 

 and to the general structure of the earth. They are 

 usually separated by geologists into two grand divi- 

 sions, distinguished by the names of primary and 

 secondary. 



The primary rocks are mostly composed of pure 

 crystalline matter, and contain no fragments of other 

 rocks. ' 



The secondary rocks or strata consist only partly 

 of crystalline matter, and contain fragments of other 

 rocks and strata, and often abound with the remains 

 of vegetables and marine animals, and sometimes 

 contain the remains of land animals. 



The primary rocks are generally arranged in 

 large masses, or in layers vertical to, or more or less 

 inclined to the horizon. 



The secondary rocks are generally disposed in 

 strata, parallel or nearly parallel to the horizon. 



* It is scarcely half a century since Geology began to be cul- 

 tivated scientifically ; the prior theories of the earth could only 

 be regarded as amusing speculations, unsupported by existing 

 phenomena. 



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