FLOOR.] 
MINERALS. 
49 
Among the rarer minerals, attention may be called to the line Div. II. 
specimens of a variety of Freieslebenite, from Hiendelencina, in Case 12. 
Spain; also to Fireblende and Xanthocone, the latter containing a 
sulpharsenate of Silver, combined with the tri-basic sulpharsenite of 
that metal. 
Division III. Compounds of the Halogen Elements. Div. III. 
This next principal division of the Collection is also subdivided into Cates 13 
the simpler compounds, and a more complex section of Salts. Among 14. 
the former will rank Calomel, Salammoniac, Common Salt (Sodium 
chloride), and Sylvine, the corresponding potassium chloride, the two 
latter being crystallised in large cubes and cubo-octahedra. With 
these are arranged the chloride, iodide and bromide of Silver, and Case 13. 
the mixtures of these inter se which are kept secluded from the d 
light. The crystal forms and colour suite of Fluor spar exhibited 
in Case 14, form a series as remarkable for beauty as any in the 
Collection. 
The Salts in this division are represented by certain double Sect. ii. ^! 
fluorides, of which the most important is the Greenland mineral Case 14. 
Cryolite. It is the sodium fluo-ahiminate, and is represented by some 
excellent specimens in its crystallised form. 
Division IV. Compounds of Oxygen. Div. IV. 
Cases 15, to- 
The remaining division consists of Minerals of which Oxi/gen is a 60. 
constituent ingredient, class necessarily large on a planet with an atmo- 
sphere consisting in considerable proportion of this chemically energetic 
element. The rocks which constitute the earth's crust, are aggregates- 
of minerals falling under this chemical division. Here, as in the pre- 
vious divisions, we distinguish the more simple kinds of combination, 
from the more complex; and though such a distinction as is expressed', 
by a section of oxides and a section of salts is a difficult one to de- 
fine with logical precision, it yet serves the object sought in a system 
of classification, by bringing together compounds that most closely 
resemble each other, the different classes falling into a natural 
sequence, nearly in the order of the simplicity of their chemical formulse. 
The first section of this chemical division, the Oxides, will be found Section i, 
arranged in Cases 15 to 2G, those containing the greater proportion of 
equivalents of oxygen following after those that contain fewer. Com- 
mencing with basic types of oxides, we pass through certain compara- 
tively neutral oxides (among which we must look for those members of 
the section which possess the most equivocal claim to a place in this 
section); and we then come to the higher oxides which act the part 
of acids. 
The oxides include several very important minerals. First in order 
among them is Cuprite, the red oxide of Copper, cuprous oxide. It 
E 
