On Crystallography. 69 



It frequently happens that the cavity in which a mineral 

 is formed contains other minerals of an anterior existence, 

 which afterwards serve it as a support when its formatiua is 

 completed. Frequently also the m'jlecules of several minerals, 

 suspended at the same time in one and the same liquid, pro- 

 duce cotemporaneous bodies. Hence the mutual adherence 

 of several minerals; those kinds of penetrations, in virtue of 

 which they are often as it were interwoven or dovetailed into 

 each other; those mixtures of molecules of several ditFerent 

 bodies; and all those sportive positions, all those varieties of 

 conditions and aspects presented to the observation of the 

 naturalist by a continual change of contrasts and shades. 



Every mineralogical collection presents numerous exam- 

 ples of these accidental combinations ; and although the 

 chief object of the mineralogist is to classify bodies from, 

 considerations independent of their natural arrangement, it 

 is nevertheless not a matter of indifference for hini to know 

 what are the other substances which adhere most usuallv to 

 such and such species of stone or metal, and their indica- 

 tion should have a place in the history of the substance with 

 which circumstances have associated them*.' But the ob- 

 servation of masses frequently of stupendous size, 'in which 

 the respective arrangement of the minerals results from an 

 operation of Nature on a grand scale, is the object of a di- 

 stinct science called ^eo/o^'y, which cannot be studied except 

 ty travelling. 



[To be continued.] 



• The French word gaiigue has bogn applied to stony substances which 

 accompany metallic veins, and matrix to substances whicii sup;>o."t, or con- 

 tain imbedded in them, other stony substance;^, or of a nature not metallic. 

 I thought it right to give an extension to the word i;.T!:^oe, by applying it in- 

 discriminately to the supports or to the envelopes of a mineral, whatever be 

 in nature. Thus, wc say tiiat such a variety of caibonatcd linie has a ijuvtis 

 Kr if-: trinigue. 



E3 .■ XI. Pro. 



