34) PHYSIOGRAPHY. CLASS II. 



lar, sometimes impalpable, often very distinct. The 

 fracture of impalpable compositions is uneven or even. 



OBSERVATIONS. 



1. Although the subspecies distinguished among the 

 varieties of the species Blende have been denominated after 

 their colours, yet they do not depend entirely or solely upon 

 these colours. The colours of yellow Blende are green, yel- 

 low, or pale reddish-brown ; its varieties possess the high- 

 est degrees of transparency which occur in the species. The 

 red and brown colours of the brown Blende are darker, and 

 its degrees of transparency lower than in the preceding sub- 

 species. The varieties of Hack Blende are either black and 

 opake, or they are blood-red. Brown Blende has been far- 

 ther subdivided into foliated, radiated, and fibrous brown 

 Blende. Simple varieties and compound ones, consisting 

 of granular individuals, are contained in the first of these 

 divisions ; columnar compositions, in which the individuals 

 are still discernible, in the second ; and very thin columnar 

 or impalpable compositions originating from them, which 

 assume various imitative shapes, are comprehended in the 

 third division. In the columnar compositions the individuals 

 often present in the cross fracture the even faces of regular 

 composition parallel to a face of the octahedron. Three of 

 the faces of cleavage may be easily obtained parallel to the 

 axis, and produce with the above mentioned faces of com- 

 position a regular six-sided prism. On account of the great 

 facility with which the faces of composition may be obtain- 

 ed, it is more difficult to observe the inclined faces of clea- 

 vage, which nevertheless are very distinct, and produce 

 with the vertical ones the dodecahedron, as the real form of 

 cleavage of the species. The exact distinction of the Wer- 

 nerian subspecies of yellow, brown, and black Blende, re- 

 quires a great deal of practice, and can be acquired only em- 

 pirically, and even then many varieties will occur that ren- 

 der the distinction impossible. This is a sure though eai- 

 pirical demonstration that the distinction itself is useless. 



