331 
VI. Tue RELATIONS or THE Rock Ty»rs. 
In the Sep d table the mineral constitution of 
the rock types 
sign is iididbtén the presence of di mineral as a 
constant feature, and often in relative abundance. 
The sign — indicates that the mineral is irira pre- 
sent. 
two combined, +, indicate that varieties of the one 
rock type may show the variation indicated : — 
$| isi i ; 
n . [4 eo a : . € 
Rock Type. | S | $ gees 3 | 3 $ 2151313 
a B zb MH 2 e E B E & E 
alae S ato « Sis | <4] a 
Granite + | "S + +| + 
Microcline T 
aum. | oS + | * (Calcio) 
Albitites .. " Pto. D p Tto 
and with a transition into a coarser 
pegmatites. 
Pe egmatites appe 
they are typically coarser graine 
range of accessory minerals, 
generally assignable to the grea 
izers during their crystallization. : 
These rocks represent the residual magma obtained by 
fractional diyatallisaón, whether by sinking of cr als, 
g 
ar to differ from aplites only in this, ced 
d, and often contain a wl 
these characteristics bung 
ter concentration of mineral- 
the cooling of the crystalline mass, is in 
joints so formed. Where differentiation of the granitic magma 
followed different lines, we have aplites socia with 
lamprophyric rocks in complementary relationship. 
A review of the literature on granite € indicates that 
these are dominantly potassic, or sodi-potassi 
Of ^y in associated with basic rocks our E awid has 
uring the last few years. Such aplites may occur 
