June, 1907.] THE VICTORIAN NATURALIST. 29 



chalcedonic and ordinary milky quartz. Its occurrence suggests 

 an extensive silicification and replacement of the original rock. 

 It perhaps represents a hydrothermal phase of the acid volcanic 

 activity represented by the rhyolites. 



At Observation Point, a rocky outlook, 5,000 feet in height, 

 on the ridge under consideration, and about five or six miles south 

 of the Tamboritha track, a great panorama is obtained. Some 

 interesting structural features can be reviewed here in the light of 

 previous observations, and in conjunction with many suggestive 

 features which can be recognized from this point. 



It is clear that the broad general structure of the extensive belt 

 of Upper Palaeozoic rocks stretching north between the Avon and 

 the Macallister valleys from the plains, and extending well up 

 towards the divide, is that of a denuded anticlinal fold of 

 considerable width. The axis of this great anticline extends in a 

 northerly direction along a line somewhat to the west of Ben 

 Cruachan, and through a point about midway between Tamboritha 

 and Wellington, continuing on for an undetermined distance to 

 the north, but visibly indicated by the opposing scarps well 

 beyond a point to the west of Snowy Bluff. The crown of this 

 anticline has been greatly denuded, most particularly along the 

 southern portion, where a long tongue of Lower Palaeozoic rocks 

 has been exposed, probably stretching continuously north from 

 the Macallister River, near Glenmaggie, well into the Upper 

 Wellington valley, a distance in a straight line of about 30 miles. 

 Observation Point lies on a ridge between the head waters of the 

 Upper Wellington and the Moroka, and almost due east of 

 Tamboritha. Here much less denudation has affected the axial 

 line, and the rhyolites outcrop almost continuously, forming a 

 belt of elevated broken country lower than the great table-land of 

 Tamboritha to the west, but rising at Observation Point to 5,000 

 feet above sea level. Here, at a point where such features would 

 be expected, the rhyolites show indication of anticlinal folding. 

 On either hand the opposing scarps of the mountain ridges show 

 clearly the features of a denuded anticline. Further evidence of 

 the continuity of the fold was obtained by supplementing the 

 evidence shown in Murray's sketch map of the southern portion 

 of this area. Tlie eastern limb of the anticline can be traced 

 continuously south along successive scarps with an easterly to 

 south-easterly dip slope, from Snowy Bluff through Wellington 

 and Mt. Hump along the Avon watershed to the plains. The 

 western limb is well developed along the Macallister River, and 

 has been examined well up the valley, past the Caledonia junction. 

 Ample evidence of extensive north and south faulting is also to 

 be found along this line. The western limb along its southern 

 portion appears to have suffered denudation more severely than 

 the eastern. It is consequently much shorter, and is not met 



