294? DISCOURSE ON THE STUDY 



said to have effectually accomplished it ; and its 

 difficulty may be appreciated by the small number of 

 simple minerals, or minerals of perfectly definite and 

 well-marked characters, which have been hitherto 

 made out. Nor can this indeed be wondered at, 

 when we consider that by far the greater portion 

 of the rocks and stones which compose the external 

 crust of the globe consists of nothing more than 

 the accumulated detritus of older rocks, in which the 

 fragments and powder of an infinite variety of sub- 

 stances are mingled together, in all sorts of varying 

 proportions, and in such a way as to defy separ- 

 ation. Many of these rocks, however, so com- 

 pounded, occur with sufficient frequency and uni- 

 formity of character to have acquired names and to 

 have been usefully applied; indeed, in the latter 

 respect, minerals of this description far surpass all 

 the others. As objects of natural history, there- 

 fore, they are well worthy of attention, however 

 difficult it may be to assign them a place in any 

 artificial arrangement. 



(330.) This paucity of simple minerals, however, 

 is probably rather apparent than real, and in pro- 

 portion as the researches of the chemist and crys- 

 tallographer shall be extended throughout nature, 

 they will no doubt become much more numerous. 

 Indeed, in the great laboratories of nature it can 

 hardly be doubted that almost every kind of che- 

 mical process is going forwards, by which com- 

 pounds of every description are continually forming. 

 Accordingly, it is remarked, that the lavas and 

 ejected scoriae of volcanoes are receptacles in which 

 mineral products previously unknown are constantly 



