GABBSOS OF EAST SOOKE AND ROCKY POINT, 
41 
with the compounds in which these oxides existed in solution, 
under the existing conditions of temperature and pressure. The 
solutions were not, however, in equilibrium with the gabbro, 
hence the minerals of the gabbro were metasomatically replaced. 
In this way the gabbro became enriched, particularly with iron, 
also with magnesia soda, and probably to a small extent with 
silica: and became impoverished in alumina and lime.'*" 
The aplitic solutions did not react so readily with the gabbro 
as did the hornblendizing solutions, and although the tendencies 
of the alteration can be observed in many places, it might be 
difficult to find one in which alteration has been carried to its 
limit, and the gabbro completely transformed to pure aplite. The 
evidence as to the composition of solutions drawn from a con- 
sideration of the composition of the solid with which they are 
in equilibrium is not, therefore, available; but fortunately this 
can be obtained directly, as much aplite is present in the form of 
fissure fillings. Analysis 3 represents one of these, an average 
aplite vein, selected because it represents at once the solid that 
was in equilibrium with an aplitic solution and the result of an 
ideally complete aplitic alteration. As detailed in the previous 
paragraph, the presence of each oxide in the aplite indicates that 
it must have been present in the solution. The proportions were 
different, however, from those of the hornblendizing solutions, 
for whereas the latter added to the gabbro magnesia, iron, and 
soda, with some silica, and removed only alumina and some lime, 
the former added silica and soda in larger amounts, and almost 
completely removed iron, magnesia, and lime. The hornblend- 
izing solutions must have been more concentrated than the 
aplitizing, at least in iron, lime, and magnesia and perhaps in all 
constituents. 
Relative Physical Conditions of Vein-Deposition. 
As regards the relative physical conditions of deposition of 
the two types of veins, it is probable that the aplites were 
deposited from cooler, more dilute solutions than were the horn- 
blendites. The aplites were of later formation, for before the 
deposition of the aplites began the deposition of the hornblendites 
