BY C. A. SUSSMILCH AND H. I. JENSEN. 161 



iii. Physiography and Topography. 



These mountains are situated on tiiat portion of the western 

 tableland which forms the divide between the watersheds of the 

 Lachlan and Macquarie Rivers. The tableland has a general alti- 

 tude of about 3000 feet, and is a continuation of one of the Blue 

 Mountain peneplains described by Mr. E. C. Andrews.* In his 

 first description he refers to it as the Lithgow Plain, but sub- 

 sequently called it the Blue Mountain Plain. f The earlier name 

 is too local for such an extensive physiographical feature, and, in 

 our opinion, it would be preferable to call it the Orange-Blue 

 Mountain Plain. Between the Canobolas and the Blue Mountains 

 numerous residuals of an older peneplain occur in the form of 

 long ridges and isolated hills. These appear to reaoli a general 

 altitude of about 3600 feet, and would correspond to the second 

 level in the Blue Mountains referred to by Mr. Andrews, and 

 which he called the Blue Mountain Plain. As this name has 

 now been taken for the lower level (3000 feet level), we would 

 suggest the name of the Clarence Plain for this level. 



Standing on top of the Canobolas and looking eastward, one 

 can see several isolated and apparently flat-topped residuals of a 

 still higher level, which appear to exceed 4000 feet in altitude. 

 These probably belong to Mr. Andrews' Jenolan Plain. 



The 3000 feet tableland (Orange-Blue Mountain Plain), which 

 in this district has been cut out of the folded Silurian and 

 Devonian strata, is intersected in all directions by numerous 

 shallow, mature valleys, from 100 to 200 feet deep. The town- 

 ship of Orange lies in one of these mature valleys, and the valleys 

 of tlie present canon-cycle head into them. 



The Canobolas Mountains ))roper cover an oval area, which has 

 a maximum diameter of about 12 miles, and extends from the 

 Orange-Forbes Railway line on the north, nearly to Cadia on the 

 south; and from the Great Western Railway on the east, to the 



* Records Geol. Survey N. S. Wales, 1904, Vol. vii., Part 4. 

 t Andrews, B.E., B.A. — An Introduction to the Physical Geography of 

 New South Wales. Published by W. Brooks & Co., Sydney. 1905. 

 12 



