BV W. N. BENSON^ W. S. DUN, AND W. R. BROWNE. 305 



sarily to l)e separated from the grtnip of Carboniferous igneous roeks. Its age is, 

 therefore, uncertain . 



Sills of keratophyre occur in the Kuttung' Series and can be traced along 

 the eastern scarp of the ridges north of Currabubula. One very interesting sill 

 occui-s immediately south of Duri Peak. It extends in the felspathic tuifs in por- 

 tion 255 for about half a mile, then turns sharply and runs as a dyke up the slope 

 to the west, cutting several bauds of conglomerate (or tillite) and turns once mors 

 into a sill in the Lower Glacial Beds at a horizon more than a thousand feet 

 higher than the part of the siU in portion 255. A little to the south of the dyke 

 which thus connects the two portions of the sill, there is a second dyke extending 

 downwards from the upper moiety of this twofold sill, till it reaches the Duri 

 pyroxene andesite, which, however, it does not traverse, though it seems to be 

 represented by an extension of the same dyke of keratophyre on the opposite 

 eastern side of the Duri andesite. There is here evidence of the contemporaneous 

 origin of at least one group of dykes and sills of keratophyre. South of this, 

 similar dykes are found to extend upwards into the sills of which they were per- 

 haps the feeding channels, and one of these appears to intersect tlie hornblende 

 andesite described above. 



South (if Currabubula Creek they appear in the Middle and Upper portions 

 of the Kuttung Beds, and have been noted in portions 212, the north-western 

 corner of 229 and elsewhere. With these we may perhaps class a sheet of felsitic 

 rock which makes a striking feature in the extreme north-west of the area 

 mapped, occurring in a iissure wliich runs parallel to the Currabubula Creek 

 fault zone. 



(6) Intrusions of less regular form. The most striking of these is perhaps 

 that which occurs in the Werrie basalts immediately west of Currabubula. Ap- 

 pearing beneath the alluvium of Currabubula Creek about a mile north-west 

 of the railway station, it extends to the south-south-east and becomes 700 yards in 

 width, and splits to the south into several thick sills- which appear in the decom- 

 posed basalts exposed in the railway cuttings. The rock of which these are com- 

 posed appears to be a normal keratophyre, but in the centre of this laccolitic in 

 trusion it is a quartz keratophyre, with a peculiar interstitial development of 

 quartz. Quartz is also found in the rock of the two following masses which invade 

 the Kuttung rocks. The smaller lies in the lowest portion 'of the series in the 

 south-eastern extremity of the region mapped, and just below the main sill of 

 andesitic pitchstone. Though its southern extremity has not been mapped, the 

 lenticular outline of the northern extremity suggests that the mass is probably a 

 laccolite. 



The larger mass lies in the valley of Werrie's Creek between Kingsmill's Peak 

 and Mount Soma. It is a roughly circular area about a mile in diameter, and as 

 it truncates sharply the planes of bedding of the grits and conglomerate on the 

 southern flanks of Mt. Soma, it may be a small boss rather than a laccolite. Its 

 southern margin has not been closely examined. It is invaded by a narrow dyke 

 of pyroxenic keratophyre. 



(c) Dykes. The dykes consist of a very varied assortment of i-ocks, quartz 

 keratophjTes, keratophyres, trachytes, latites, lamprophyre, andesites, dolerites 

 and basalt. As yet they have not been sufficiently studied to determine their 

 chronological relationships. In the northern portion of the map they have a 

 general north-easterly trend, but in the southern ])ortion they run more nearly 

 east and west, tending thus to radiate from the volcanic centre of AVarragundi, 



