98 ON THE TABLES OF MODIFICATIONS. 



classes of primary ones, with each other, and with 

 their respective primary forms ; as he will thus obtain 

 a general view of the entire series of simple secondary 

 forms belonging to all the known classes of the pri- 

 mary. 



In these tables, not merely the observed modifications 

 of 'crystals , but all the numerous modifications of which 

 each class of primary form is susceptible, while in- 

 fluenced by the law of symmetry, are reduced into 

 classes, and arranged in an orderly series and I have 

 added some of the observed instances of departure 

 from this law, in the production of peculiar and 

 anomalous secondary forms. 



From a general view of the tables, it will be seen 

 that the first classes of modifications are those on the 

 solid angles of the primary form ; these being suc- 

 ceeded by the modifications upon the edges, beginning 

 in all cases with the simplest change of form. 



It has been already stated, that each of the classes 

 of primary forms, may comprise many individual forms 

 "belonging to as many different species of minerals ; 

 which individual forms, with the exception of such 

 as belong to the cube, the regular tetrahedron and 

 octahedron, and rhombic dodecahedron, will be found 

 to differ from each other in the measurement of some 

 of their angles, or in the ratios of some of their 

 edges. 



Each of the classes of modifications, excepting those 

 which produce tangent planes, and which consequently 

 admit of no variation, may also comprise a series of 

 individual modifications; which individual modifications 

 will be found to differ from each other, in the angles 

 at which the modifying planes incline on the adjacent 

 primary planes. 



Thus the series of modifying planes which would 

 be comprehended under class b, in the table of modi- 



