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MUSEUM BULLETIN NO. 30 . 
itself, and the acid varieties form a series varying in composition 
from a quartz diorite to a very siliceous granite. Then followed 
a period of faulting with production of large shear zones in the 
gabbro, accompanied by much jointing. Through the fissures 
and shear zones rose very hot solutions highly charged with 
mineral matter, which altered the rocks with which they came 
in contact to masses of hornblendite. Another period of jointing 
ensued, and through this set of- fissures there again rose solutions 
which formed aplitic fissure and replacement veins. After these 
were formed, a second period of faulting took place, in which the 
stresses relieved themselves along the earlier-formed shear zones 
now filled with hornblendite, and through the brecciated and 
crushed hornblendites the solutions which deposited the chalcopy- 
rite ores ascended. Finally, further minor jointing took place. 
The relations of the hornblendites and aplite to each other 
and the main gabbro mass were studied in some detail. It was 
shown that these are the pegmatitic after-effects of the intrusion, 
the last exhalations of the cooling magma. The hypothesis is 
advanced that the emission of such solutions from a magma is a 
continuous process throughout the whole period of cooling, but 
that the escape of. the solutions so formed is governed by the 
more or less accidental occurrence of movements able to joint 
the intrusive and thus afford channels of flow. The load of such 
solutions always includes all the constituents of the rock from 
which it has originated ; although the amounts of these vary; and 
are dependent on the temperature of the solutions, and probably 
also on other conditions of which we are ignorant. The composi- 
tion of the veins formed by them, and their metamorphic effects 
on the wall rocks, therefore, vary according to the time in their 
history when they were enabled to make their escape. In the 
case under consideration, opportunity for escape occurred at two, 
or possibly three, periods, owing to the frequency with which 
jointing and faulting movements affected the stock, and veins 
of different composition thereby resulted. 
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