333 
The mode of differentiation of ie teo rocks can be con- 
sidered azs the e folowing heads : 
A. THE ORIGIN OF THE MICROCLINE—ALBITE APLITES. 
e microcline-aplites and albite-pegmatites are the only 
intrusions within the confines of the granite as exposed. No 
basic dyke-rocks were seen by the writer. In the country rock, 
some miles from the granite contact, Prof. aes vak 2) has 
reported, a basic dyke of diabasic compositio . The writer, 
X Mp was unable to visit the locality Ee his visit. 
spite the abundance of aplite associated with the 
panite, there appears to be a scarcity of other satellitic types 
of intrusion, such as those of lamprophyric type, which, if 
ht 
field evidence must be taken as it stands, for we have no 
Warrant to assume that such lamprophyric types are present 
but still uncovered. 
s evidence is therefore suggestive that the microcline 
imr: are direct VAS cd of the granite magma by a process 
of fractional crystalliza 
he aplites as now BARS in the granite came into 
their position during the cooling and contraction of the 
crac d fissures. In this respect, therefore, the aplitic 
intrusions resemble those characteristic of so many granitic 
masses. 
The origin of the albite rich pegmatites which are 
developed in minor amount within the granite remains to be 
treated. 
B. THE ORIGIN OF THE ALBITITES. 
It has been noted in the previous discussion that aplites 
associated with basic rocks were often highly sodic, but not 
invariably so. In the case of the Willoughby pegmatites, the 
Sodic type is associated only with granite. eir sodic nature 
—in some cases they consist almost wholly of albite—is, how- 
ever, no reason for genetically connecting them with Ver 
rocks. Here again field evidence warrants no such assertion. 
Their mode of occurrence is esse ntially as sm du 
cutting the granite. Their possible modes of differentiation 
can be considered under three heads :— 
(a) Aey represent an immiscible Tos phase separating 
rom the residual magma 
20) W, p onekin Trans. Roy. Soc. S. Austr., 1903, vol. 
: xxvii. pt. 1., p. 82. i 
