152 BIOLOGY OF SNOWY RIVER AREA 



tains phenocrysts of quartz and felspar, up to £ inch long, set in a 

 salmon-pink ground mass. Xenoliths, if present, are very rare. 

 Many large boulders show evidence of spheroidal weathering, 

 similar to granite. The rock decomposes to a poor gritty soil, 

 which does not support a dense vegetation on the hillsides. The 

 western limits of this quartz porphyry are not known; a track 

 south of Currie Creek was followed westwards for at least one 

 mile without any apparent change in the nature of the rock. 



This outcrop is probably similar to quartz porphyry described 

 by Howitt from the Cobboras, Mt. Wombargo and Mt. Statham; 

 and, as he suggests, these masses are probably "the denuded 

 stumps of volcanoes" which lie on an old meridional fissure ex- 

 tending from the Cobboras to Buchan. 



(b) Volcanic Rocks. — South of Currie Creek, approximately 

 11 miles west of the road, the quartz porphyry described above is 

 in contact with a fine-grained volcanic rock, containing phenocrysts 

 of quartz in a fine-grained ground mass which, although altered, 

 shows a well defined flow structure (Plate 12, upper). Angular 

 xenoliths are common, and in places the rock shows evidence of 

 secondary silicification. 



To the east of this locality, all the Snowy River porphyries so 

 far examined consist of volcanic rocks, and include tuff beds and 

 great masses of agglomerate. The eruptions producing this great 

 thickness of material appear to have been of the explosive type, 

 rather than quiet eruptions producing vast flows of lava. 



Huge masses of agglomerate stand out above the surrounding 

 vegetation at a locality known as Bare Rock, situated south of 

 Boundary Creek in the parish of Wulgulmerang East. These 

 masses are composed mainly of boulders of quartz porphyry 

 which stand out in relief on the weathered surface of the rocks. 

 Many of the boulders appear to have been rounded before being 

 incorporated in the agglomerate. Masses of similar agglomerate 

 are exposed on the high rugged cliffs, where the colony of rock 

 wallabies was located above the Suggan Buggan River. 



In all cuttings on the road down to the Suggan Buggan River, 

 the rock appears to be very uniform, and contains phenocrysts 

 of quartz and pink felspar with abundant fragments of sedi- 

 mentary rock set in a grey or pinkish ground mass. This rock 

 is very hard and massive, and was responsible for considerable 

 trouble during road building operations. The same type of rock 

 occurs north of Little River, near its junction with Wombargo 

 Creek, and also along the Forest Commission Road which is being 

 cut from the main road just north of Boundary Creek westwards 

 to a peak known as Seldom Seen. 



