680 NOTES ON THE NATIVE FLORA OF N. S. WALES, X., 



Gudgeiiby, there are fairly level interspaces showing little or no 

 dissection, and in some cases containing swampy areas. 



If we block out a model in the form of a great irregular 

 wedge, and consider the Molonglo River as the northern edge of 

 the wedge, a horizontal section the full width of the Territory 

 and extending south to the southern boundary would give us the 

 length of the wedge, the length of the base would be the width 

 of the Territory in the south, while the width (depth in this 

 case) of the base would vary from perhaps 3,000 to about 4,300 

 feet in the south-west corner. In viewing this great irregular 

 so-called wedge, which is higher along the western side, we find 

 it is scored longitudinally into more or less deep ravines, along 

 which flow the Cotter, Paddy's, Gudgenby, and Murrumbidgee 

 Rivers. The deepest of these gorges is occupied by the Cotter 

 River, which at Thomas Oldfield's (Portion 2, Parish Fergus, 

 County Cowley) is roughly 3,600 feet above sea-level, so that 

 the river has here, under Mount Bimberi, entrenched itself to a 

 depth of nearly 2,700 feet. The Murrumbidgee occupies the 

 shallowest of these channels, and, in parts of its upper portion, 

 around Tharwa, flows at the eastern foot of the mountains 

 through an almost mature valley, so far as the eastern side is 

 concerned, while it has cut gorges of varying depths down 

 stream. 



Geological Formations.* 



Quoting from Mr. Pittman's map, it may be said that the rocks 

 within the Federal City Site consist of Upper Silurian sand- 

 stones, quartzites, shales, tuffs, clay-slates, and several outcrops 

 of limestone, while the igneous rocks are crystalline tuffs and 

 lavas, quartz-porphyries, and quartz-felsites. 



In the western and southern portions of the Federal Territory, 

 a considerable area is composed of granite of a fairly siliceous 

 character. Granite rocks are common around Tharwa, Boo- 



* See a detailed "Geological Survey of the Site of the Federal Capital 

 of Australia," by Edward F. Pittman, A.R.S.M. (1910). Also, a "Report 

 on a Geological Reconnaissance of the Federal Territoiy," by D. J. 

 Mahony, M.Sc, &c., and 't. Griffith Taylor, B.Sc, &c. (1913). 



