54 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
accurately, dacitic volcanic material but also of boulders of the meta- 
morphic series, the granodiorite and the earlier Lower Edie type 
porphyry. Volcanic breccias were formed presumably by the same explo- 
sive outbursts, the distinction between the two being principally that 
the breccia is composed almost entirely of schist and fragments of the 
early porphyries, little volcanic material being recognisable. The 
boulders and rock fragments of which it is composed, too, are more 
angular although they still show a slight degree of rounding. The 
constitution of the boulders in the agglomerate and the breccia shows a 
general relation to the nature of the underlying rocks. Just west of 
Edie Creek, granite, porphyry and schist are prominent. The breccia 
above Golden Ridges is composed of slate and Lower Edie porphyry, 
while down towards the Bulolo River, only porphyry and dacite are 
found. The inference is that several different volcanic vents existed. 
Field relations at Enterprise Mine near Edie Creek and in the 
Golden Ridges area suggest that the blue breccia is a later phase of the 
volcanic activity. It overlies the principal agglomerate formation, which 
in the few places where they are found together appears to pass upward 
into it without any definite line of demarcation. The agglomerate is much 
more wide-spread than the breccia, which is confined to a few localities 
of restricted extent, whereas the agglomerate is found up to several 
hundreds of feet thick over most of the Lower Bulolo and part of the 
Watut Valley. In places along the divide between the two rivers, flows 
of obsidian are associated with the agglomerate, and narrow bands of 
rhyolite occur similarly in the Golden Ridges area. Indigenous boulders 
within the agglomerate are essentially similar to the porphyry suite, 
differing mainly in the fineness of the ground mass, which is crypto- 
crystalline or even glassy, and in their generally extrusive aspect. Flow 
structure is sometimes developed, quartz is relatively less abundant, but 
in sufficient quantities to classify the rock as a dacite. Crystallisation 
appears to have been well advanced before it reached the surface, as 
would be expected from its manner of occurrence. A notable feature 
of these volcanics is the predominance of pyroclastic material and the 
almost complete absence of flows. 
The latest porphyries are intrusive into the volcanic breccia, but 
it is difficult to establish exactly when effusive activity began. The 
constituent boulders of the breccia and the agglomerate should establish 
definitely their place in the igneous sequence, but owing to the close 
petrological similarity of the porphyries of the different ages, and the 
generally weathered and altered condition of the breccia where it out- 
crops, it has not so far been possible to establish more than the fact that 
the Lower Edie type porphyry is a conspicuous constituent of the 
volcanics, and no definite proof exists that any other porphyries are 
present. This problem is made more difficult by the fact that the breccia 
and the agglomerate are not found very close to the main mineralised 
area at the head of Edie Creek so that the absence of porphyries of the 
Upper Edie type from the breccias and agglomerates, if it could be 
established, would still not be conclusive evidence as to their relative age 
