852 



THE GEOLOGY OF THE NANDEWAR MOUNTAINS, 



appears that the trachyte has flowed over an eroded surface and 

 infilled the valleys. The present valleys, such as that of Bullawa 

 Creek, represent the high ground before the period of the erup- 

 tions; 'the thin flows capping the sandstones here having soon 

 become denuded away, erosion has rapidly carved out valleys in 

 the softer sandstones and shales. 



North by east to north-north-east from Ritter's farm The 

 Razorback attains a height of 3,050 feet and is capped with 

 vesicular amygdaloidal trachytes. Further eastward, about J or 

 J a mile from Mount Odin, sandstones and conglomerates dipping 

 N.W. at 5-10° cap the range at an altitude of from 2,950 to 

 3,050 feet (Fig.5). The change in formation makes an imme- 

 diate change in the forest flora, pine (Callitris calcarata 1) and 



Razor BACK 



Bas.c S.Jl 



BdStc Laccolite 



«£tg|^- 



0.,oSE:ar3o° 



Fig. 5, — Section across Bullawa Creek at Dawson's, in a general N. and S. 

 direction. F, fault; r, trachyte or bostonite; cr, sandstone. 



oaks (^Casuarina Luehmaniii and Camhagei) replacing the box 

 and gum. Smaller cappings (relics) of trachyte occur here too. 

 On descending The Razorback, walking southwards towards the 

 junction of Bullawa and Oakey Creeks, a large sill or dyke of 

 basic rock is met with. The outcrop is 300 yards wide. Below 

 this basic mass trachyte porphyry becomes the countr}^ rock, and 

 represents a laccolitic offshoot of the Mt. Odin mass (Fig.5). Mt. 

 Odin is precipitous on the northern, western, and southern 

 flanks, and has a steep slope to the east towards the gap between 

 Bullawa and Pound Creeks. The cliffs consist of sandstone beds 

 alternating with trachyte or porphyry sills. My brother in pro- 

 ceeding up the creek called on my map Thor's Gully, observed 

 numerous sills of trachyte and dolerite intruding sandstones. 



