44 
MUSEUM BULLETIN NO. 30. 
of lime. As cooling continued, the iron-magnesia compounds 
reached their limit of solubility, and through reactions with the 
wall rock the homblendite veins were formed. The crystalliza- 
tion of the components which entered the homblendite left the 
solutions relatively enriched in water and silica, and to a less 
extent in soda. During this period of homblendite formation, 
the remainder of the solutions probably escaped beyond the limit 
of the intrusive, as they left no record of their presence. As 
the gabbro mass continued to cool, the precipitation of lime, 
magnesia, and iron went on at progressively greater depths, until 
the solutions, as they passed the surface of the mass, were 
sufficiently cooled -and enriched in silica, soda, and water, to 
precipitate the constituents of aplite. With progressive cooling, 
the soda precipitated in smaller and smaller proportion, so that 
the central part of the aplite veins is largely or wholly quartz. 
Conditions Governing Escape of Solutions. 
The previous description indicates the probable course of 
events had the exhalation and escape of the solutions from the 
cooling gabbro been a continuous process. But it was not a 
continuous process, for although the formation and segregation 
of the solutions themselves undoubtedly went on without cessa- 
tion at some point or points within the borders of the intrusive 
as it gradually cooled and crystallized, the escape of these solu- 
tions was controlled by the fortuitous formation of the necessary 
channels by jointing or faulting. Hence the composition of the 
veins as they are* actually found simply gives us a clue to the 
composition of these magmatic waters at two periods. Had 
jointing taken place at other periods, veins of quite different 
composition might have resulted. Earlier jointing would prob- 
ably have yielded veins whose mineralogy approached that of 
contact metamorphic deposits; later jointing, veins of pure 
quartz. The solutions which deposited the copper ores in this 
stock may have been a later phase of these same magmatic 
waters, although on account of the poverty of minerals other than 
chalcopyrite in the copper deposits definite information on this 
point is so far unobtainable. 
