LI 
162 
On account of the viscosity the actual size of the crystals 
would be small, for diffusion currents would not move 
sufficiently rapidly to supply the growing crystal. 
e conditions above described probably represent the 
“‘labile’’ state of undercooling, as described by Ostwald and 
Miers.ü9 "The micropegmatite, on this view, represents the 
composition of the hypertectic rather than the eutectic point. 
ear thé summit of the fissure chamber, crystallization 
would be initiated, as this is the point of maximum under- 
cooling due to the combined effects of cooling and of 
compounds of boron (boric acid) e would originate 
throughout the depth of the fissure chamber and, viscosity 
rmitting, would gradually rise in the magma c er, 
ment and, possibly, by coalescence of two or more bubbles. 
At this stage the magma chamber is pictured as filled with a 
layers. _ With the removal of anhydrous minerals at t : 
crystallization level, additional gases would probably be se i 
free. The bubbles, in ascension, on reaching the network 0 
o these in the form of bubbles. The gases released on 
fluid 
hich 
sr pi 
mass containing a network of crystal silicates, some of w 
: t i6 
fi i i 
` fissure chamber. The volatile components present 1n the g r 
phase are assumed to have been, predominantly, water an 
boric acid 
. With a further reduction in temperature these mineral- : 
izers take up an active róle and enter u : teraction 
stage. The felspar becomes unstable, and in an inte 
^ . e 
tourmaline is produced ?7. situ, th 
Whe sion ron compounds : 
: felspar being partially or completely. replaced, according t° 
JR pase pee a E UI a AR : 
_ O09 Vide the numerou. rs by Mi d his co-workers: 
S o SENE papers by Miers and his istorY 
eterences to these are quoted b A. Harker, Natural H 
