ORE DEPOSIT THEORIES. 233 
exceptionally ; rutile also occurs in tin veins, as at Schlac- 
kenwald and Schénefeld in Bohemia. 
4c. In both kinds of vein sulphides are present in large 
quantities, but this is not specially characteristic of these 
deposits. 
4p. In both types of vein the principal vein-minerals con- 
sist of silicates, which is of genetic signification, in so far 
that the presence of silicates in tin veins is one of the dis- 
tinctions between them and ordinary silver-lead veins. 
With regard to the details of the mineralogical differences . 
between the two types of vein, there are also many striking 
analogies. Thus, in both types of deposit we meet with 
large quantities of mica—in the tin veins, alkali mica (often 
lithia mica); in the apatite veins, on the other hand, mag- 
nesia mica. Quartz and tourmaline are found in both 
types of vein, but in tin veins in much larger quantities. 
The difference lies in the fact that the mineral components 
of the tin veins—quartz, alkali mica, tourmaline, topaz, 
beryl, fluorspar, &c.—are in the apatite veins represented 
by magnesia mica, enstatite, hornblende, scapolite, &c. 
5. In both classes of vein we meet a halogen element 
in very large quantities. In the tin veins fluorine, with 
occasionally a little chlorine; in the apatite veins chlorine, 
_ with sometimes more or less fluorine. In the tin veins the 
quantity of fluorine which is present in the various fluor 
minerals (fluorspar, alkali mica, topaz, tourmaline, and 
fluorapatite) is, as a rule, very great, both relatively to the 
chlorine and absolutely. Thus, in tin veins and the adjoin- 
ing metamorphosed wall-rock there is probably more fluorine 
than tin present.* ; 
6. In the metamorphosed wall-rock of the tin veins a 
much more considerable transport of material has taken 
place than in the corresponding wall-rock of the apatite veins. 
We may explain this phenomenon by the fact that fluorine 
(in hydrofluoric acid or fluorides) is a much more powerful 
agent in the tin veins than is chlorine (in hydrochloric acids 
or chlorides) in the apatite veins. The whole scapolitisation 
metamorphism is to be referred to an impregnation with 
chlorides, especially sodium chloride under pressure. 
7. In the tin veins, as also in the apatite veins, the 
minerals characteristic of each vein recur also in the wall- 
rock. Thus, we find in the tin veins, both in the veins 
themselves and in the adjoiming rock, quartz, alkali mica, 
*In a later article, Vogt, quoting J. H. Collins, states that in 
the tin veins in Cornwall the amount of fluorine is about 100 
times as great as the amount of tin by actual weight. 
