24 MEMOIR OF WERNER. 



these primary bases. The mysterious force of crys- 

 tallization is the only one that presents any resem- 

 blance to the generative power: it determines in like 

 manner the composition ; but this is only within cer- 

 tain limits. Recent experiments have evinced that 

 there are substances whose crystalline virtue is such, 

 that they constrain very considerable quantities of 

 different substances to accommodate themselves to 

 their form ; and it has been long- observed in nature, 

 that crystals, in-ell respects alike, those of sparry 

 iron, for example, may contain more or less of iron 

 or of lime, as there may be in two animals of the 

 same species a greater or less quantity of fat, of ge- 

 latine, or of the earth of the bones. 



In mineralogy, therefore, crystallization must be 

 regarded as the fundamental principle of the species, 

 as far as it addresses itself to our sight ; but in an 

 immense majority of minerals, the crystalline form 

 is not visible, and, in such cases, the composition is 

 very far from enabling us to determine it ; for the 

 latter is more variable than in the crystals, and im- 

 pure intermixtures corrupt it more easily. No al- 

 ternative, then, is left, but to have recourse to the 

 properties which are most closely connected with 

 the fundamental principle, viz. cleavage, which is 

 only one of its phenomena, fracture, hardness, lustre, 

 and the effect of the body on the touch, which are its 

 more or less immediate consequences. 



This plan Werner has pursued, not perhaps proceed- 

 ing exactly upon these reasonings, but led by that 



