342 
whereas in ordinary nepheline-syenites this ratio does not ex- 
ceed 1'1!. The agpaites are thus in a position within the ne- 
pheline-syenite group which is somewhat analogous to that 
occupied in the family of rhyolites by the pantellerites. 
Iron is generally present in large quantities, but owing to 
the excess of alkali it does not appear as iron ore in the rocks: 
it crystallizes instead as egirine, arfvedsonite, and ainigmatite. 
Even in the black kakortokite (К, in Fig. 32) with 25:4 per cent. 
of iron oxides there are no iron ores. Alkalies are also un- 
usually high, while magnesia is wanting, and lime in most cases 
is low. A very characteristic feature is the presence of zir- 
conia and chlorine. In some extreme differentiation products 
of the agpaitic magma these elements are present in consider- 
able quantities: thus, the red kakortokite contains 5 per cent. of 
zirconia, and some varieties of the naujaite consist of almost 
pure sodalite. 
A glance at the curves given in Fig. 32 will show that 
the agpaitic rocks vary from melanocratic to leucocratic. In 
this report the melanocratic agpaites have been classified under 
three heads according to their structure: — (1) lujavrites, char- 
acterized by ægirine and arfvedsonite in needle shaped crystals; 
(2) kakortokites, which are coarse-grained with stumpy anhedra 
of ægirine and arfvedsonite and rather thin tabular crystals of 
felspar; and (3) sodalite-foyaite, a very coarse-grained rock 
with thick tabular crystals of felspar and a considerable quantity 
of allotriomorphic sodalite. The name which has been given to 
the last mentioned rock is not very adequate, and may be re- 
garded as only provisional. Chemically the rock is closely re- 
lated to the tavite of Ramsay, but structurally it is quite different, 
1 The values of the ratio (na — k):al for each of the types which have 
been analyzed for this report, are given at tne end of the volume in 
the table of analyses calculated at 100 per cent. In the agpaites of Ili- 
mausak the ratio varies from 12 to 2'!, while in ordinary nepheline- 
syenites the ratio is from OS to 1'1. 
