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THE GEOLOGY OF THE OANOBOLAS MOUNTAINS. 



By C. a. Sussmilcii, F.G.S , and H. T. Jensen, D.Sc. 



(Plates vii,-ix.) 



A. General Geology and Physiography. 



PAGE. 



i. Introduction ... ... ... ... ... ... ... 157 



ii. Petrography ... ... ... ... ... ... ... 158 



iii. Physiography and Topography 161 



iv. Descriptive Geology ... 163 



1. The Lava-FIows and Tuffs 163 



2. The Dykes and Necks 169 



3. The Order of Eruption of the Lavas 170 



4. xAge of the Volcanic Eruptions. .. 171 



B. Petrology 172 



C. Comparison with other Areas, with some additional 



Notes on those Areas (by H. I. Jensen) , ... 192 



General Geology and Physiography, 

 i. Introduction. 



The Canobolas, or Canoblas, are an isolated group of mountains, 

 about seven miles to the south. east of the town of Orange, N.S.W., 

 and lie at the junction of the three Counties of Bathurst, Well- 

 ington, and Ashburnham. Rising about 1600 feet above the 

 level of the surrounding tableland, they form a conspicuous feature 

 of the landscape, particularly when viewed from the west. 

 Situated, as they are, so close to the main Western Railway line 

 and in the neighbourhood of such a large town as Orange, it is 

 surprising that they have received so little attention from 

 geologists in the past. 



In 1878, the late Mr. C. S. Wilkinson (then Government 

 Geologist) visited the Canobolas, and came to the conclusion that 

 tlie "Old Man Canobolas" had at one time formed a point of 

 volcanic eruption on a somewhat grand scale. 



In 1890, Prof. T. W. E. Bavid visited the Old Man Canobolas, 

 and subsequently contributed a brief note to the Proceedings of 



