496 J. T. Jidson: 



when he states that the south-flowing stream passed over the 

 Beenak Gap probably at a time when the surface of the coun- 

 try was some 600 feet higher than at present (1, p. 113). 



If Prof. Gregory's view be correct, the Yarra would not be the 

 main stream until the capture of the various north and south 

 streams mentioned by him. By the time however the Nillum- 

 bik Peneplain was formed, there could be no doubt that it 

 was the principal river of the area. The conditions previously 

 stated would therefore hold good in its future development ; 

 and I see no reason to doubt that such development was on the 



The Influence of Hard Rocks in the Evolution 

 of the Topography. 



The remarks made on the complexity of the Yarra illustrate 

 this subject very well. A wider comparison is also available, 

 and may now therefore be discussed. Such discussion, however, 

 is almost entirely based on the map to be presently referred 

 to, and not as the result of much personal observation. 



It is proposed to compare the Yarra Basin with adjoining 

 basins, and principally with that of the Upper Goulburn. The 

 latest geological map of Victoria (a portion of which with 

 some details omitted and an alteration of the boundaries of the 

 basins near Mt. Baw Baw, is reproduced) shows, as of course 

 is well known, that the Main Divide runs east and west, and the 

 principal streams consequently to the north and south. 

 Notable exceptions to this general rule are the Yarra and the 

 upper portion of the Goulburn. These are east and west 

 streams. It is also to be noticed that as the Main Divide ap- 

 proaches from the east Mounts Howitt and BuUer, it becomes 

 forked, the northern prong extending through Mount BuUer, 

 Tabletop, the Strathbogie Ranges, and thence to Trawool. 

 The southern prong runs south from Mount Howitt to a little 

 north of Mount Useful, and thence westward through Mounts 

 Matlock, Arnold and St. Leonard to Mount Disappointment. 



The southern px'ong is the actual Main Divide, and is along 

 the northern boundary of the Yarra Basin. The Upper Goul- 

 burn has an opening at its western end connecting with the 



