361 
simplest supposition is perhaps that the recurrent layers have 
originated in consequence of repeated variations in pressure. 
Each reduction in the pressure may have caused the dissocia- 
tion of a certain quantity of volatile matter from the magma, 
and this process in its turn may have caused the crystallization 
of a certain quantity of the magma!. 
The above attempt at the interpretation of the peculiar stra- 
tified structure of the coarse-grained kakortokites may be sum- 
marized thus: — 
The entire series, comprising more than one hundred in- 
dividual sheets, may be divided into a smaller number of groups 
of layers (about 40), in which each group consists of an upper 
white sheet and a lower black one, and betveen them as a 
general rule an intercalated red sheet or a transition zone rich 
in eudialyte. Each group of sheets is supposed to have ori- 
ginated by differentiation in situ owing to a separation of cry- 
stals under gravity. The repetition of the groups indicates that 
the consolidation process was of recurrent or intermittent char- 
acter, and it is suggested that the repetition is a kind of abys- 
sal reflection of the intermittence which characterizes igneous 
surface activity. 
Of course this mode of abyssal stratification is only pos- 
sible where the crystallizing magma possesses an exceptionally 
high fluidity. It is, therefore, important to note that the stra- 
tification here considered is not the only fact which suggests a 
very fluid condition of the magma: a number of other peculiar 
features of the agpaitic rocks of Ilimausak, which have been 
discussed in the preceding sections, point to the same conclu- 
sion. In ordinary viscous magmas the variations of pressure 
etc., caused by contemporaneous volcanic eruptions, must of 
course also be supposed to influence the crystallization of the 
1 Compare Е. Rinne, Durch Entgasung bewirkte Krystallisationen in 
Schmelzflüssen. Neues Jahrbuch für Mineralogie, 1909, II, p. 129. 
