44 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
Amongst the gaseous and liquid constituents of the mother-liquor 
carbon dioxide is the principal mineralizer. The others are water, 
chlorine, fluorine, and boron. These keep alkalies in solution. The car- 
bonic acid is responsible for keeping a large amount of silica in the liquor, 
and the haloids account for the presence of various heavy metals 1 . Conse- 
quently, when at the comparatively low temperature of between 500° 
and 1,000° C. the mother-liquor consolidates, it may contain a consider- 
able number of minerals containing fluorine, chlorine and boron, as well 
as others in the formation of which the haloids play a part. Amongst 
such minerals are tourmaline, topaz, tin, wolfram, tantalite, &c. 
A study of the pegmatitic dykes rich in sheet mica shows that most 
of them have quartz blows developed within them. Often such blows 
outcrop strongly on the surface. They contain no mica. Around each 
such quartz blow there is usually a zone of graphically intergrown quartz 
and felspar, a eutectic zone. Outside this there is a zone of massive 
crystalline felspar. The eutectic and felspar masses rarely contain any 
vestige of mica as inclusions. Odd interstitial veinlets of later origin 
may contain some mica. 
When quartz blows are absent along the outcrop there are usually 
lenses or bands of quartz along the hanging-wall, and sometimes sub- 
sidiary bands within the dyke. 
Around and between the quartz blows, as described, the main body 
of the dyke consists of a miarolitic coarse aggregate of quartz, felspar 
and mica, in which good books may be developed in a manner described 
later. Often the best books occur just outside the massive felspar, and 
moulded on the felspar. 
The mica books often contain inclusions of other minerals such as 
tourmaline, rutile, quartz, felspar, &c., which spoil the value of the mica. 
The inclusions show that the sheet mica was the last mineral to form. 
In normal granites the order of crystallisation is usually that of 
decreasing basicity. Mica commenced to crystallise before felspar, 
though it might continue to grow while the felspar was forming. Mass 
action and low content of pneumatolytic solutions are the causes of 
crystallisation, in accordance with decreasing basicity of minerals, in 
muscovite granite. 
My predecessors in geological investigation on the mica field adopted 
the sequence of crystallisation of muscovite granite as that of pegmatites 
also. Hence they had to invent a second period of intrusion to account 
for the quartz blows. 
Actually the order of crystallisation of pegmatite dykes is, accord- 
ing to my investigations, as follows: — 
'(T) Quartz blows, 
(2) Eutectic intergrowth of quartz and felspar, 
(3) Massive felspar, 
(4) Miarolitic pegmatitic mixture of quartz, felspar and mica, 
(5) Mica and quartz. 
The pegmatites do not follow the same order of crystallisation as 
granites but behave like hydrous solutions, under great temperature and 
pressure, but nevertheless much lower than those under which granites 
