365 
From what has just been said the following conclusions 
may be drawn: — 
(1) There is geological evidence that the augite-syenite at 
Iviangusat has dissolved some sandstone, and has produced a 
hybrid rock: soda-granite. 
(2) The composition of the hybrid rock cannot be calcu- 
lated as a simple addition mixture of the component rocks. 
On the contrary, it must be supposed that the assimilation of 
the sandstone has been accompanied by processes of differen- 
liation or diffusion’. When evidences for and against the 
assimilation theory are discussed the circumstance that assi- 
milation may produce differentiation is not seldom overlooked; 
though it appears to be in harmony with the fact that assimi- 
lation will change temperature and sequence of crystallization, 
and specific gravity of the magma. 
(3) The quantity of solid material which has been absorbed 
by the magma is probably not less than half the weight of the 
absorbing magma, but by reason of the differentiation (men- 
tioned in (2)) it cannot be calculated until we have a more 
detailed knowledge of the differentiation processes which have 
taken place. 
The arfvedsonite-granite of Ilimausak. — The hybrid soda- 
granite of Iviangusat is of special interest from another point 
of view. As already mentioned it agrees chemically and in all 
mineralogical essentials with the arfvedsonite-granite of Ilimau- 
sak (compare analyses 1 and 2, р. 114). The latter rock mass 
both in size and in mode of occurrence has quite the char- 
acter of an ordinary abyssal rock. The arfvedsonite-granite 
type, moreover, though by no means a common rock, is known 
from several foreign localities; and is usually regarded as a 
normal differentiation product of magmas belonging to the 
ТА. Harker, Natural History of Igneous Rocks, 1909, р. 358. 
