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in their nature are associated together, and that the 

 strata immediately beneath the soil contain materials 

 which may be of use for improving it, a general view 

 of the nature and position of rocks and strata in na- 

 ture, will not, I trust, be unacceptable to the scientific 

 farmer. 



Rocks are generally divided by geologists into 



two grand divisions, distinguished by the names of 

 primary and secondary. 



The primary rocks are composed of pure crystal- 

 line matter, and contain no fragments of other rocks. 



The secondary rocks, or strata, consist only part- 

 ly of crystalline matter ; contain fragments of other 

 rocks or strata j often abound in the remains of vege- 

 tables and marine animals ; and sometimes contain 

 the remains of land animals. 



The primary rocks are generally arranged in 

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

 inclined to the horizon. 



The secondary rocks are usually disposed in 

 strata or layers, parallel, or nearly parallel to the 

 horizon. 



The number of primary rocks which are com- 

 monly observed in nature are eight. 



First, granite j which, as has been mentioned, is 

 composed of quartz, feldspar, and mica ; when these 

 bodies are arranged in regular layers in the rock, it is 

 called gneis. 



Second, micaceous schistus, which is composed of 

 quartz and mica arranged in layers, which are usually 

 curviiineal. 



