161 
develops an hypothesis of differentiation of volcanic rocks in 
la arge part based on the lowering of freezing point accom- 
a 
gmas. 
e phenomenon of resorption, common in phenocrysts of 
hypabyssal and volcanic rocks, has AES been attributed by 
some writers to a reduction in pressure consequent on injec- 
tion or eruption. There can be little doubt that this lowering, 
which never exceeds a few degrees per 1,000 atmospheres, (12) 
is enormously overweighed by the decreased fusibility conse- 
vert on removal of volatile components. (15) 
ing to the loss of volatile constituents and to a rare 
d g temperature, equilibrium would 
violently disturbed, and the residual magma conditions would 
ecome ura Some of the components of the fluid pre- 
viously near or at aen freezing point would then become 
2) Uniform Passer of cour UM postulated here. The 
diferential effects of uniform and non-uniform pressure are dis- 
tU m detail by Jeluieton and Adams. Amer. Jour. Sci., 35, 
> 
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physico-chemical E as appli a 
temperatures and res. "There n be little doubt, therefore, 
that vd melting lepression is dependent on the concentration oí 
the y atile compon ent. 
Which is. thus undercooled, with 
— aa to ane silicate, although the 
peratur has bui slightly 
c" "The illustration is, of 
neg ‘purely diagrammatic 
: complete for the solution in | 
_(water-silicate). A r M 
