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262 



MINERALOGY. 



[Sect. VIII. 



dom with which the particles of the isolated minerals thus 

 formed could often adjust themselves, the main mass 



We 



retaining its general structure, is liighly interesting, 

 have seen crystals of garnet, perfectly formed, amid the 



contact with granite, the 



gram 



beds of the sandstone retaining their original shape, and 

 the mechanically-produced grains well distinguishable. 

 The component parts of andalusite have often been 

 gathered together in such a manner to form that mineral 

 in altered rocks, that the resulting crystals have pushed 

 aside mica and other substances. 



have chiefly referred hitherto to minerals found 

 crystallized, or produced under the conditions proper for 



We 



the 



e 



alone or entangling some other substances. Many im- 

 portant mineral substances occur, so that, whatever may 

 be the form of their ultimate molecules, they appear to us 

 in mass, sometimes forming beds mingling with others, 

 or occupying clefts in rocks ; occasionally constituting por- 

 tions which have separated out from the bodv of the rock, 

 as m the instances of the nodules previously mentioned. 

 In these various form.3 many minerals are found, some 



such as iron ores, including 



being ores of the useful metals 



bog-iron among them, ard iron nv. Ites, valuable for the 

 sulphur in it. As filling clefts in rocks, mingled with other 

 matter, many ores of lead, tin, copper, &c. Other 



tances, also employed for various purposes, are obtained 

 in the massive state, such as rock-salt, gv-psum, and coal. 

 For these minerals qualitative chemical researches will 

 be found valuable, it being desirable to test the com- 

 position of many substances, which may offer certain 



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