232 PROCEEDINGS OF SECTION C. 
of apatite veins. This metamorphism is most conspicuous 
where the veins traverse their own respective mother rocks. 
This may, perhaps, be referred to the fact that when the 
veins were being formed, the eruptive rock, although already 
consolidated, was still in a highly heated condition. 
4. From a mineralogical standpoint, we meet with a 
whole series of very remarkable analogies, and further, also 
several equally characteristic differences. The tin veins, 
which are, on the whole, distinctly separate, both mineralogi- 
cally and geologically, from the common silver-lead veins, 
are characterised mineralogically and chemically by the 
following substances : — 
Stannic acid (together with tungstic, tantalic, niobic, 
and sometimes titanic and zirconic acid), 
Sulphides, 
Silicates (in large quantities), 
Borates, 
Phosphates (apatite, &c.), 
Fluorspar, &c. 
The apatite veins, on the the other hand, contain— 
Titanic acid (together with iron oxide and a little 
zirconic acid), 
Sulphides, 
Silicates (in large quantities), 
Phosphates (apatite in large quantities). 
4a. Apatite, with other phosphates, is common to both 
types of ore deposit, with the difference, that in the apatite 
veins the former is the principal component mineral, while 
in the tin veins it plays, on the whole, a minor part. Still, 
apatite is a very characteristic component of tin veins, as 
proved by the fact that apatite or other phosphates 
constantly occur in tin veins over the whole world, whereas 
it is absent entirely, or almost entirely, in the silver-lead 
veins of Freiberg, Clausthal, Kongsberg, &c. It is true 
that phosphates are, as a rule, only sparsely distributed in 
tin veins, nevertheless there are also several exceptions to 
this; for example, the tin veins in Dakota contain a large 
amount of apatite and other phosphates, and even in the 
granite itself, as in Estremandura in Spain, we meet occa- 
sionally with apatite veins which, in a broad genetic sense, 
we may regard as tin veins. Thus, we may follow step by 
step the transitions of the apatite veins in gabbro to the tin 
veins in granite. 
4n. The stannic acid of the tin veins is represented in the 
apatite veins by titanic acid, which often occurs in large 
quantities. In place of cassiterite, we here meet with 
rutile (together with titanic iron ore, titanite, &c.), but 
