40 PHYSIOGRAPHY". CLASS II. 



kind of regular composition is frequently repeated, 

 contiguous to all the terminal edges of II 1 , as 

 in Fig. 140., or still farther, since two new indivi- 

 duals may again be joined to every one of the for- 

 mer group, A great number of individuals are 

 often joined in that manner. 2. Face of compo- 

 sition parallel, axis of revolution perpendicular to a 

 face of R 2. This mode of composition forms 

 the Supplement to the preceding one, but it is far 

 Jess frequent. 8. Face of composition parallel to 

 a face of R -f- oo, axis of revolution perpendicular 

 to it. If the individuals are continued beyond the 

 face of composition, then the composition is parallel 

 to all the faces of 11 -f oo. Massive : composition 

 granular, of various sizes of individuals, strongly 

 connected. If the composition becomes impalpable, 

 fracture is uneven, even, or flat conchoidal. Plates, 

 superficial coatings. 



OBSERVATIONS. 



1. The difference between the Light and Dark Red 

 Silver^ though originally founded on the different tints 

 of colour and streak of the two minerals, and on their 

 lustre, which is dependent upon them, is deeper rooted 

 in the essence of these bodies than it would appear at first 

 sight. The forms of the Light Red Silver have not yet 

 been ascertained with sufficient exactness ; they do not 

 seem, however, to be very different from those of the Dark 

 Red Silver, and also the peculiarities in their crystallisa- 

 tions are common tp both. There is no difference in their 

 hardness. The specific gravity of the two substances, how- 

 ever, is considerably different, being circumscribed, as far as 

 our present information goes, within the limits of 5-8 ... 5:9 



