336 
anorthite, these latter being selectively locked up in the inner 
zones of plagioclase. 
The non-volatile constituents of the residual magma thus 
consisted essentially of'quartz and microcline and subordin- 
ately slightly calcic albite.. 
With the renewal of crystallization in the residual magma 
quartz and microcline were early precipitated, the magma 
being thus constantly depleted in these constituents. That 
some albite crystallized during this period is also evidenced by 
the presence of subordinate albite, associated with the micro- 
cline and quartz. This albite was still slightly calcic and with 
erystallization its composition approached pure albite. The 
Nearing the completion of crystallization of such a magma 
pool, the residual liquid would have markedly changed in 
composition through such selective crystallization. This 
residual liquid depleted in potassic constituents would there- 
fore have become highly sodic. r 
By the opening of fissures in the surrounding rock this 
residual liquid, derived by fractional crystallization from the 
dominant potassic magma, was strained off from the crystalline 
mass and solidified in the occupied fissures. : 
__ Derived by such a process of fractional crystallization this 
residual liquid would be:—(i. Predominantly sodic; (ü.) 
characterized by an increased concentration of mineralizers. 
This process of differentiation receives considerable sup- 
port from a study of the albitites. 
muscovite-albitites appears to be secondary. This is prin- 
i iden 
ers 1s pneumatolytic pr is intimately 
ntration of mineralizers d 
lization of t hattering of albite plates 
TORN allization. The muscovite, indeed, 
ent the hydrolysis of potential microcline-felspar. 
