ON THE TABLES OF MODIFICATIONS. 101 



the entire series of secondary forms, resulting from 

 any given class of modifications, are similar through- 

 out the series, it is not invariably so. Among the series 

 of secondary forms resulting from particular classes 

 of modifications of the rhomboid, there are some con- 

 tained within scalene triangular planes, and others, 

 belonging to the same class, contained within isos- 

 celes triangular planes. These differences will gene- 

 rally be pointed out in the tables. 



The series of new solids, or complete simple second- 

 ary forms, resulting from each of the classes of modi- 

 fications, will be described in the tables under the 

 appellation of new figures. 



It is to be observed that very few of the individual 

 modifications belonging to the several classes, have 

 yet been found to exist among crystals. And it is 

 doubtful whether all the classes even have been 

 hitherto noticed. 



The figures of the primary and secondary forms, 

 given in the following tables, are not to be regarded 

 as representations of crystalline forms of any par- 

 ticular minerals, but as exhibiting a type, or general 

 character, of each of the classes of primary forms, and 

 of the modifications belonging to each of those classes. 



A position is chosen for the figure of each of the 

 primary forms, which is supposed to be constant 

 throughout the series of modifications belonging to 

 each. The position of the greater number will be 

 readily comprehended from the figures themselves, 

 but there are a few which require a short explanation. 



The figure of the right rectangular prism has its 

 greater edge horizontal, and its largest plane is sup- 

 posed to be a terminal one.* 



* The horizontal lines here referred to, are those which are parallel 

 to the upper or lower edjjei of the page, 



