COLLECTION OF MINERALS. 275 



and sometimes having no outward resemblance 

 to each other. But this singular metamorphosis, 

 submitted to simple laws, and the effects of 

 which may be calculated, confines itself to modi- 

 fications of the external appearance, without 

 altering the mechanism of the internal structure, 

 which is constant and uniform in every variety. 



Such is the action of these laws, to which 

 nature is subjected, that, when undisturbed, she 

 inclines to produce the most simple forms, and 

 those best characterized by regularity and sym- 

 metry. This operation is called crystallization^ 

 and the bodies so formed, crystals. But it fre- 

 quently happens, that local circumstances and 

 disturbing causes interfere, to interrupt or de- 

 range the ordinary progress : hence incomplete 

 and irregular forms are produced, either mis- 

 shaped structures, into which the primitive form 

 insensibly degenerates, confused aggregations of 

 foliations or needles, fibres or grains, or lastly, 

 masses entirely compact. 



Every mineralogicai collection should possess 

 a series of species methodically distributed, and 

 each species should have its varieties placed 

 according to their degree of perfection. The 

 collection in the Museum presents a picture of 

 the mineral kingdom, divided into four great 

 classes, according to the method of M. Hatty. 



18. 





