CHAPTER II. 
PLUTONIC AND METAMOEPHIC EOCK8. 
(GEANITB, SYENITE, AND ACID CEYSTAILINE EOCKS.) 
Miueral Areas— viz., Herljerton Tin Field, Kangaroo Hills and Running Creek Silver and Tin 
Fields, Annan and Bloonifleld Tin Fields, Ravenswood Gold and Silver Fields, Sellheim 
Bismuth mines, Croydon Gold Field, Etheridge Gold Field, Eidsvold Gold Field, Mount 
Ferry Copper Mine, Tenningering, Boolhoonda, Molangul, and Hormanhy Gold Fields, 
Jimna and Gooroomjam Gold Fields. 
In denoting tlie whole of these rocks, on the ground of their lithological relationship, hy 
a single colour, I am well aware that the highest purpose of a geological map is not 
served, but it seems all that can be done until a great amount of detailed surveying, 
accompanied by micro-petrographieal study, can he carried out. 
In some regions the Granites and Syenites are clearly motamorphic. In others, 
whether originally of metamorphic or of plutonic origin, they are covered hy the 
oldest fossiliferous deiiosits of the Colony. Sometimes they are intruded among 
the earlier rocks. Sheets of quartz-porphyry in the neighbourhood of Townsville 
have been intruded among rocks containing Olossopteris, and presumably of the age 
of the Bowen Eiver Coal Eield. The Hon. A. C. Gregory refers * to “ the extensive 
development of the porphyritic rocks which, rising through the Carbonaceous strata 
[Ipswich T'ormation], form the range dividing the valley of the Mary Eiver from the 
Maroochy Eiver.” 
The same Author thus refers to the porphyries of the Moreton and Darling 
Downs districts f : — “ The porphyry consists of a pale-brown paste with minute 
felspathie crystals, though it sometimes varies so as to consist of very small grains of 
quartz with minute cavities, containing oxide of iron, resulting from the decomposition 
of pyrites. Occasionally it is vesicular, and has the aspect of trachyte. 
“ The age of tins rock is greater than that of the basalts, which cut through and 
overlay it, though it often occurs that the basalt has found vent through the same 
fissures as the porphyry, and formed spurs to the more elevated masses of the older 
igneous rock, a feature which is especially developed on both sides of the Main Eange, 
near Cunningham’s Gap, where Mount Cordeaux, Mount Mitchell, and Spicer’s Peak 
are porphyry, and the subordinate ranges basaltic. 
On the other hand the age is less than that of the Carbonaceous Series [Ipswich 
Eormation], as the porphyry in all cases is found superimp)osed on the sedimentary 
strata. 
The porphyritic rock is chiefly developed in the southern portion of the 
Moreton district, wEere it forms all the remarkable peaks on the Great Dividing Eange 
from the head of Laidley Creek to the southern boundary of the Colony, and thence 
along the Maepherson Eange, which separates the Logan Eiver from the Clarence, 
Eichmond, and Tweed Eivers. 
* Report on tho Geology of part of the District of Wide Bay and Burnett. Ecp. Brisbane : by 
Authority : 187B. 
+ Report on the Geological Features of the South-eastern Districts of Queensland. Ecp. Brisbane : 
by Authority : 1879. 
