ORE DEPOSIT THEORIES. 231 
that is crude and incomplete in the details of our theories, 
the main facts of magmatic differentiation and extraction 
may be regarded as scientifically proved. This is a great 
step in advance in the theory of ore deposits. For, in mag- 
matic extraction we find an alternative process of concentra- 
tion to that which has been so carefully investigated by the 
meteoric school. The adherents of the latter school have 
shown how concentration may take place after eruptive rocks 
have solidified. The plutonic school have shown how this 
may take place before or during consolidation. The working 
agent of the meteoric school is meteoric water; the working 
agent of the plutonic school is plutonic or magmatic water. 
According to some geologists, even magmatic water is of 
meteoric origin; but this question need not be discussed in 
the present paper. As far as the origin of ores is concerned, 
they must be regarded as quite separate. 
Apatite Vems. 
Professor J. H. L. Vogt* has made an exhaustive investi- 
gation of the apatite veins which occur abundantly in 
Norway, Sweden, and Canada, and he comes to the conclu- 
sion that these apatite veins bear precisely the same relation 
to basic rocks that tin veins bear to the acid rocks. 
The following is a very free and somewhat abridged trans- 
lation of his brilliant comparison of the two types of 
veins : — 
1. Both the tin and the apatite veins represent fairly well- 
defined groups of ore deposits, both of them intimately con- 
nected with eruptive rocks: the tin veins with the acid 
eruptives—granite and its dyke-forming and effusive repre- 
sentatives; the apatite veins with basic eruptives, such as 
gabbro. 
2. The tin veins, and also the apatite veins, are certainly 
younger than the eruptive rocks with which they are con- 
nected, nevertheless, it may often be proved that the 
difference in age between the formation of the veins and the 
consolidation of the eruptive rocks is not great (the apatite 
veins are sometimes crossed by dykes of diabase, the dyke 
forming representative of the gabbro, in the same way that 
tin veins are crossed by aplite, the dyke-forming represen- 
tative of the granite). 
3. Still more characteristic for both groups of ore deposits 
is the remarkable metamorphism of the wall-rock, greis- 
senisation in the case of tin veins, scapolitisation in the case 
* Zeitschrift fur practische Geologie, 1894-95. Beitraige sur 
classification der Erzvorkommen, &c. 
