341 
of the sheets have been viscous at the same time, and thus an 
origin by successive intrusions seems to be precluded. 
The most probable interpretation of the rocks of the 
transition zone appears to be that they have been produced in 
situ by an interaction between the granitic and the agpaitic 
magmas, and that the mingling along the junction has given 
rise to reaction sheets which have crystallized at a higher 
temperature than either magma. Another theory is that the 
above explanation should only be applied to the upper and 
lower sheets, and that the middle sheet, the pulaskite, is a 
remnant of the original syenite which at one time filled the 
reservoir. The latter view is perhaps supported by evidence 
from the northeast side of Nunasarnausak, where the pulaskite 
sheet comes next to the augite-syenite of the unstratified com- 
plex. Here no boundary has been detected between the two 
rocks, but further observations are needed before the question 
can be settled. 
The адрайез. The term agpaite (see footnote р. 338) is 
here introduced as the name of a subgroup of the great family 
of nepheline-syenites. As a subgroup it is characterized by cer- 
tain peculiarities of chemical composition. The compositions 
for the Ilimausak agpaites are given in the analyses 5—15, and 
the main types are represented graphically in Fig. 31 ($, N, L, 
and K). For comparison the figure also gives the composition 
of two other nepheline-syenites, one of which (F,) may be taken 
as a representative of ordinary non-agpaitic foyaites, while the 
other (F,) is approximately intermediate between the ordinary 
foyaites and typical agpaites. 
The chemical character which distinguishes the agpaites 
from other nepheline-syenites is the excess of alkalies in pro- 
portion to alumina. Thus, if па, k, and al are the relative 
amounts of Na-, K-, and Al-atoms in the rock, the apaites may 
be characterized by the equation: 
na + k — 
SS ER 152° 
ай = 
