MINERAL VEINS, 
85 
native metal usually contains a small proportion of silver, the 
amount of which sometimes rises to a considerable extent, 
forming the species called Native Amalgam. Most of the quick- 
silver of commerce is, however, obtained from the sulphide 
known as Cinnabar or native vermilion. In Europe the most 
important mines are those of Almaden, near Cordova, in Spain, 
and of Idria, in Carniola, whilst in California valuable deposits 
of this ore occur at New Almaden. The metallurgical treatment 
of cinnabar will be noticed at p. 98. 
Arsenic. 
Case 23. — The collection of foreign ores is brought to a close 
by a few arsenical minerals. Of these the principal are the 
bright aurora-red bisulphide of arsenic called Realgar , and the 
lemon yellow tersulphide known as Orpiment, of which the 
former is the more important. Both the arsenical sulphides have 
long been employed as pigments, but for this purpose they are 
usually prepared artificially. 
LODES OR MINERAL VEINS. Wall Cases 24 to 36. 
The Wall Cases occupying the circular or north end of this 
floor are devoted to the exhibition of an instructive series of 
specimens intended to illustrate, within such a space as may be 
conveniently studied, many of the conditions under which lodes 
or mineral veins occur, and the general characters which they 
present. 
In order to understand these conditions, reference may first 
be made to the Model of a typical mining district in Cornwall, 
at present placed in the Model-room A. and numbered I. 
The two dissimilar woods are intended to illustrate the pre- 
vailing rocks of the country — granite and Milas or clay slate. 
The lines which run across these rocks are supposed to represent 
mineral lodes, containing either tin or copper, as shown by the 
different colours introduced. Anyone imagining this model to 
represent some square miles of country, across which there has 
occurred extensive cracks, either in the process of the consolida- 
tion of the rocks, or by mechanical force since the period of 
consolidation, will realize the facts, in the main, of our mineral- 
vein formations. Cracks have been formed in the rocks, and 
these fissures have served as channels for the circulation of 
subterranean waters, from which mineral matter has been 
deposited. The exact mode in which the fissures have been 
filled is, however, a subject of much speculation, but one on 
which light may be thrown by the study of such a collection of 
veinstones as is here exhibited. It will be seen that in some cases 
the minerals must certainly have been deposited from a state of 
solution, though the source of such solutions may be obscure 
