40 
CONCLUSIONS 
The earliest rocks to be intruded are dark green, fine-grained to por- 
phyritic, and, in some cases, have a trachytic texture. These rocks are char- 
acterized by large amounts of pyroxene, augite, and aegirine-augite; and by 
considerable biotite. Quartz is usually present in small amount. Albite, 
or, in the porphyritic types, potassium feldspars, or both, form up to 75 
per cent of the rock. Areas of this type of rock are scattered throughout 
the whole igneous mass; they are not confined to the edges as they would 
be if the edges represented the original, basic, and more quickly chilled 
parts of the intrusion. 
Succeeding phases are lighter coloured. The ferromagnesian con- 
stituents are less and the feldspar and quartz more abundant. The feld- 
spar phenocrysts are predominantly potash varieties, but albite is con- 
centrated in the groundmass and in many cases replaces the phenocrysts 
and even some of the larger quartz crystals. 
The final, fine-grained dyke rocks are nearly pure albite and quartz 
and within them and in the neighbouring rocks, a considerable amount of 
blue, soda-rich amphibole has been produced. In some cases small stringers 
of blue-green amphibole cut intermediate types of the syenite porphyry 
in areas where many of the late acid dykes occur. 
The rocks grade from basic types, the earliest to be intruded and which 
seem to correspond roughly with nordmarkite porphyry, through coarse 
quartz syenite porphyries to fine-grained alkali syenites. Some of the 
later phases that are particularly rich in quartz verge on granite porphyries. 
The igneous body presents highly femic phases in abundance. Feld- 
spathoid types, as far as known, are lacking. This may be due to several 
causes. The prevalence of trachytic textures among the larger masses 
of the more basic varieties is taken to indicate the action of differential 
pressure which would probably lead, as Bowen 1 suggests, to squeezing out 
of residual liquid from the parts of the magma that were already partly 
solidified. These residual liquids, judging from the nature of the later 
phases of intrusion, were rich in quartz and the alkalis, particularly soda. 
The relatively large amount of quartz in some of the more acid varieties 
may be due to a cessation of the differential pressure on the magma and 
the resultant intrusion of the residual material en masse. The great extent 
to which the original potash feldspars and much of the ferromagnesian 
material have been corroded points to a high concentration of volatile 
constituents in the residual liquids of the magma. Sodium appears to 
have played a major part in these final reactions. Additions of sodium 
after crystallization of the late phases of the intrusion, which are them- 
selves very rich in albite, is evidenced by a peculiar blue, soda-rich amphi- 
bole which cuts across, in very irregular fashion, the feldspar crystals that 
form the most acid varieties of the syenite porphyry. It also forms by alter- 
ation of green hornblende, pyroxene, or biotite where rocks containing 
these minerals have been cut by more acid dykes. These facts indicate 
that the whole mass of igneous rock has, after solidification, been acted 
upon by the volatile constituents which accumulated at that time, as a 
final end point of differentiation, and which were exceptionally rich in 
UJowen, N. L.: Jour. Geo]., Supplement, vol. 23, p. 56 (1915). 
