50 
NORTH GALLERY. 
[UPPER 
Dlv. II. Among these a large mass of resplendent crystals, of a rich ruby 
Case 12. colour by transmitted light, was presented by H. Ludlam, Esq., and 
is a unique specimen. 
Among the rarer minerals, attention may be called to the fine 
specimens of a variety of Freieslebenite, from Hiendelencina, in 
Spain; also to Fireblende and Xanthocone, the latter containing a 
tri-basic sulpharsenate and sulpharsenite of Silver; and to the series 
of minerals from the Binnenthal, including very fine crystals of 
Jordan ite. 
Div. III. Division III. Compounds of the Halogen Elements. 
Sect. i. '^•(••^aiMd^ii ••tfontf •£••!•• * •• .. . . .' u ;•. -• vjiiiii; jI 
Cases 13 This next principal division of the Collection is also subdivided into 
14. the simpler compounds, and a more complex section of Salts. Among 
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 
Case 13. these are arranged the chloride, iodide and bromide of Silver, and 
the mixtures of these inter se which are kept secluded from the 
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. 
Sect. ii. The Salts in this division are represented by certain double 
Case 14. fluorides, of which the most important is the Greenland mineral 
Cryolite (sodium aluminium fluoride), represented by some excellent 
specimens in its crystallised form. 
Dxy. iv. Division IV. Compounds of Oxygen. 
Cases 15, to . . . . . 
00. The remaining division consists of Minerals of which Oxygen is a 
constituent ingredient,^ class necessarily large on a planet with an atmo- 
sphere consisting in considerable proportion of this chemically energetic 
element. The rcnks 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 formulae. 
Section i. r ^ ne nrst sect i° n °f tn i s chemical division, the Oxides, will be found 
' arranged in Cases 15 to 26, those containing the greater proportion of 
oxygen following after those that contain fewer. Commencing with 
basic types of oxides, we pass through certain comparatively 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 in 
combining with bases. 
The oxides include several very important minerals. First in order 
