498 . J. T. Jutson: 



it is at present, especially in view of the short course of the 

 Yarra to the sea. Tlie bar however retarded denudation, and 

 enabled the rivers of the adjoining basins to annex territory 

 that otherwise would have been occupied by the Yarra. 



In support of this proposition, attention may be drawn to 

 the boundaries of the Upper Goulburn Basin, which, except in 

 the east and south-east are igneous rocks. In the south-east 

 corner, the basin abuts on to cliose of the Yarra and of the 

 Thomson. The rocks here and for some distance north and 

 south are ordovician and silurian sediments, and are prac- 

 tically homogeneous in character. 



A struggle for supremacy (on even terms as regards the 

 character of the rocks at their head waters) has taken place 

 between the three basins mentioned ; and, although the Yarra 

 has the shortest course to the sea, yet its small drainage area 

 and consequent less rapid erosion, together with the retarda- 

 tion due to the igneous bar at Warburton, have not enabled 

 it to contest for territory successfully with the other basins. 

 The battle has therefore been principally between the Upper 

 Goulburn and the Thomson Basins. 



On present knowledge the line of the original divide in the 

 district of the head waters of the Goulburn and Thomson 

 Rivers is unknown, but from the present divide's tortuous course, 

 it niay be safely asserted that it has been sul)j?cted to much 

 shifting. It would appear, however, from the general direction 

 of the divide, that it was, in the district mentioned, much fur- 

 ther north than at present ; and that by reason of the soft 

 rocks and the greater drainage area, resulting in the rapid 

 approach to base-level in its lower portion, and consequently 

 greater power of erosion in its head water streams, the area 

 of the Goulburn Basin has been increased at the expense no 

 doubt of the Thomson and Yarra Basins. "Whatever may 

 have been the actual history, if a fairly wide band of dacite 

 and granodiorite had stretched as a bar from Mt. Torbreck 

 to Mount Buller, part or most of the south-east corner of the 

 Upper Goulburn Basin may not have been included in such 

 basin. 



The fact that the Thomson and Tanjil Rivers, as shown by 

 Messrs. Kitson and Baragwanath, Jun. (IG, ]ip. S6 and 87), a{> 



