327 
structure, but changes its composition gradually from sea level 
to the top of the mountains. 
It will be seen, therefore, that the syenite can neither be 
interpreted as a contact modification of the nepheline-syenites, 
nor regarded as a dyke, but that it must have originated as 
an independent intrusion prior to the arrival of the nepheline- 
syenites. To some extent at least it must have been solid when 
the nepheline-syenitic magma was intruded, but it has had no 
chilling effect on that magma. 
If, as here asserted, the complex has come to place 
mainly by magmatic stoping the syenite can only be interpreted 
as a remnant of an older batholite, of which a great portion 
Fig. 30. Idealized section of the Ilimausak batholite, illustrating its 
complex nature. 
I The older, unstratified part of the batholite (mainly syenite). II The newer, stratified 
part of the batholite (mainly nepheline-syenite) which has partially replaced the syenite. 
has been replaced by the nepheline-syenite (Fig. 30). As the 
specific gravity of the nepheline-syenite is considerably lower 
than that of the syenite, it is probable that also the nepheline- 
syenitic magma was less dense than the syenitic magma, and 
the replacement, therefore, may perhaps have occurred at a 
time when the syenite was in a somewhat viscous state. On 
the other hand, the fragments mentioned above tell us that 
some portions of the syenite at least have been removed in the 
solid state. 
This hypothesis for the mutual relation of the stratified 
and the unstratified parts of the abyssal complex gives a satis- 
factory explanation of their distribution, both horizontally and 
vertically. On the northeastern side the nepheline-syenitic 
