348 
however, in our case does not constitute an objection, for the 
composition ofthe agpaitic magma suggests that its final temper- 
ature of consolidation was extremely low, whereas several of the 
minerals which are characteristic of agpaites under magmatic con- 
ditions have exceptionally wide temperature ranges of crystalli- 
zation’. It is, therefore, not difficult to imagine that the agpaitic 
magma during the early stage of crystallization may have been 
more fluid than are most other magmas. 
As quoted above the agpaitic sheets from above downwards 
are as follows (the figures in parantheses indicate the average 
thickness of each rock body): 
sodalite-foyaite (100 meters) 
naujaite (300 meters) 
lujavrites and kakortokites (more than 600 meters). 
The approximate mean composition of these rocks as well 
as the probable composition of the undifferentiated agpaitic 
magma (leaving out volatile matter) has been given in the table 
(p. 344). 
It is obvious from this table that the composition of the 
uppermost layer — the sodalite-foyaite — is very near to the 
average composition of the agpaites. Considering that the 
sodalite-foyaite is a very coarse-grained rock, and that only 
one analysis has been made, it can hardly be said that any 
difference in chemical composition between this rock and the 
mean agpaite has yet been proved. Provisionally, then, the 
sodalite-foyaite may be regarded as undifferentiated agpaite which 
in the upper part of the magma chamber has crystallized en- 
tirely without disturbance. 
The naujaite and the lujavrite differ from the mean agpaite 
1 This follows from the observation that sodalite, ægirine, and arfved- 
sonite, often constitute the latest products of crystallization in the same 
agpaitic rocks where idiomorphic crystals of these minerals are enclosed 
in the felspars. 
