CRYSTALLIZATION IN IGNEOUS ROCKS 185 
The order of crystallization will depend on relative masses, but will 
in every case end with a ternary eutectic. We all concede that the 
rate of growth of different crystals varies, but it does not seem 
probable that in the same solution one substance, such as quartz, 
begins solidifying before a second, say orthoclase, and also is still 
crystallizing after the latter is completely removed. Such over- 
lapping would seem to be an unusual exception to the general rule, 
of which no example has been found. Considering this point, may 
we not assume that order of cessation of crystallization gives a 
definite clue to the order of beginning of crystallization ? 
SUMMARY 
With a view of testing the conclusions as to order of crystalliza- 
tion, the author advances the following points: 
1. We cannot assume that the effects of pressure and of crys- 
tallization temperatures may be considered negligible in the case 
of rhyolite and granite (effusive and deep-seated rocks). There- 
fore it is doubtful that we can assume the same order of crystalliza- 
tion or the same end-products. 
2. We must recognize the importance of the mineralizers, not 
only as affecting the physical condition of the magma, but also its 
molecular arrangement, and consequently its manner and possibly, 
order of crystallization. 
3. Comparing the order of crystallization in solutions and alloys, 
we find that the order of cessation of crystallization gives a definite 
clue as to the order of beginning of crystallization, consequently 
overlapping both of the beginning and the cessation of crys- 
tallization of any substance by another seems improbable. 
The author is indebted to Professor M. F. Coolbaugh for 
valuable suggestions. 
