DOMAIN XII. VOLCANIC. 291 



much as to say, that Botany can only be 

 studied in the roots, or Zoology from the 

 legs of animals ; that History may be stu- 

 died in a book of chronology ; or that, in 

 short, any science may be attained with 

 complete inattention to its chief objects. 

 For a laborious study, and even the most 

 nice discrimination of lithologic character- 

 istics, is indispensable ; otherwise the key- 

 stone may happen to be the weakest, and 

 the whole edifice may sink in ruins. The 

 treatises of Dolomieu on different rocks, 

 published some years after in the Journal 

 de Physique, though tedious, prolix, and 

 ill-digested, like all his writings, are the 

 best and most scientific of his productions. 

 But, on the other hand, our celebrated 

 mineralogist is certainly mistaken, when he 

 asserts that siliceous stones undergo no 

 change in the heat of volcanoes ; for the 

 white or grey lavas, with a base of felspar, 

 are among the most common, and are some- 

 times interspersed with mica, so as to show 

 that the parent rock was a felspar mixed 

 with that substance ; while the mottled or 



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