Lava Residuals. 157 



Significance of the Cross-lateral. 



The speculations arising from a consideration of the immense- 

 power gained by the cross-lateral by successive captures, are impor- 

 tant and interesting. It is suggested that the Great Valley of 

 Victoria! may have had its beginning in this way, and although 

 crustal movements, block faulting and other factors may have ulti- 

 mately contributed to its formation, portion of it at least east of 

 Melbourne may be thus accounted for. How powerful the Hallam 

 Creek actually was may be conceived by the fact that its flood plain 

 is in many parts a mile wide, although, through beheading, it now 

 carries a mere trickle. The part played by this stream in the sedi- 

 mentation of the Carrum Swamp was considerable. 



IV. — Distribution of Residuals and Classification of 



Valleys. 



Confines of the two systems. 



The Older Basalt residuals of the area dealt with in this paper- 

 are along the trend of Pre-Older Basalt valleys (Fig. 3) belonging 

 to two well-defined systems, namely, the Western Port and the 

 Port Phillip. At the cessation of volcanic activity the watershed 

 separating these two systems extended from Arthur's Seat to> 

 Frankston, and was due to the resistance offered by the meta- 

 morphic rocks at the contact of the Palaeozoic sedimentary and 

 igneous series. Between Frankston and Dandenong it was com- 

 posed of less resistant sediments, probably of Palaeozoic age. 

 From Dandenong it followed the metamorphic rocks, to the west 

 of that town, to Wheelers' Hill, thence to Vermont, thence through- 

 Ringwood to the quartzites running parallel to Brushy Creek, 

 Its continuation was the line of hills formed by these quartzites 

 through Mt. Graham, Big Hill, Conical Hill, and Bald Hill, to 

 about eight miles east of The Gap, beyond which point it has not 

 been defined. This watershed has been referred to in this paper 

 as the Wurunjerri'^ Range. Parts of the drainage system of the 

 Yarra referred^ to by Prof. Gregory as the basins of the Middle- 

 and Upper Yarra are here assigned to the Western Port system. 



1 Vide Bibliog., No. 4. 



2 The Wurunjerri tribe inhabited the Yarra basin. 



3 Vide Bibliog., No. 4. 



