230 PROCEEDINGS OF SECTION C. 
veins on the other. The series, granite-porphyry dykes, 
aplite dykes, pegmatite veins, tin veins, is in perfect agree- 
ment with this theoretical proposition. 
The details of the process by which the magma becomes 
differentiated into sub-magmas containing varying amounts 
of water have given rise to much speculation, but there 
is reason to hope that very soon a sound working hypothesis 
will be evolved which will explain the division of the magma, 
not only into highly aqueous and slightly aqueous sub- 
magmas, but also into acid and basic sub-magmas. The 
subject is too complex to be discussed in this paper. 
Whatever the determining causes are then, the granite 
magma is believed to separate itself into sub-magmas, con- 
taining differing amounts of water. Into the most aqueous 
of these, Arrhenius concludes, on chemico-physical grounds, 
that the ions of carbonic acid, hydrogen sulphide, chloric, 
fluoric, boric acids, silica, the alkali metals, less frequently 
the alkaline earths and the metals, iron, zinc, lead, copper, 
and tin would become concentrated. This process has been 
termed “acid extraction” by Vogt, because fluorine and 
chlorine are believed to play the principal part in effecting 
the concentration or extraction of the metals. 
The aqueous portion is, of course, very small in con 
parison to the rest of the magma. Its amount depends 
upon the original amount of water in the magma, and no 
doubt in many cases there may not be sufficient water in 
the magma to produce the division at all. Where it is 
formed, however, the aqueous portion would be much more 
mobile than the other part, and would retain its fluid state 
at much lower temperatures. Owing to the consolidation 
of the granite, much of it would be expelled through cracks 
and fissures, and coming up into the cooler portions of the 
granite would first of all precipitate the normal constit- 
uents of the granite, the quartz, feldspar, and mica. The 
strong acids, still in an excessively hot condition, would 
attack minerals of the wall-rock, and a series of complex 
reactions would take place which, after the experimental 
results of Daubrée, we may well imagine would account for 
all the phenomena which we meet with in tin ore deposits. 
When dealing with phenomena which are so far removed 
from our observation as the processes of consolidation of 
deep-seated eruptive rocks, which take place at such high 
temperatures and pressure that they cannot be imitated in 
the laboratory, it is not surprising that our notions of these 
processes should be somewhat vague. This is certainly the 
case with our modern theories of magmatic differentiation 
and extraction. Nevertheless, although there may be much 
