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alkali series. The soda-granite of Iviangusat, thus, though it is 
of hybrid origin, produced at moderate depth through the as- 
similation of sandstone by an alkali-syenitic magma, is an 
instance of a rock possessing the composition of a normal 
abyssal rock. | 
The theoretical question thus arises, whether or not it is 
possible that the Ilimausak granite could have come into exist- 
ence as a consequence of assimilation processes which were 
similar to the processes indicated by the small granite bodies 
which envelop the sandstone fragments at Iviangusat. Harker 
raises the general objection to any theory of absorption of sedi- 
ments on a large scale ‘that it demands an enormous amount 
of heat to raise the solid rock to the point of melting and to 
melt them, and no source of this heat is indicated’. In the 
case here considered an objection of this kind can scarcely be 
maintained. The sediments dissolved are not those in the roof 
of the batholite, but fragments which are slowly sinking through 
the magma, and such fragments may be rather intensely heated. 
| Further, since the soda-granite at Iviangusat not only surrounds 
the sandstone fragments, but also occurs as veins in the 
syenite (p. 53), we are taught by actual observation that the 
temperature of the consolidation of the hybrid rock was lower 
than that of the original magma. The amount of heat, contained 
in the syenitic magma, under these conditions must be supposed 
to have been sufficient to melt considerable quantities of sand- 
stone; just as salt even at a low temperature may be dis- 
solved in water. 
In this way it seems probable that the syenitic magma has 
been able to dissolve considerable quantities of sandstone. The 
rock interpreted as an assimilation product has a lower specific 
gravity and a lower consolidation temperature than the syenitic 
magma, and it seems to be within the bounds of possibility that 
! Natural History of Igneous Rocks, 1909, p. 339. 
