132 Robert A. Keble: 



along them and assisted by a system of domestic piracy, with com- 

 parative rapidity, became the main streams with the original 

 streams as tributaries. These new streams thenceforth assumed the- 

 characterstics of lateral streams. 



The widening of the lateral streams had the effect of gradually- 

 restricting the width of the residuals. Tributaries of lateral 

 streams (termed ''minor laterals"), having their source on and 

 cutting back into a residual, tended ultimately to sever it into a 

 number of , isolated residuals, which became more and more isolated' 

 as the streams in question developed. A stream that has actually 

 breached a residual is termed a "cross stream." During the 

 Intermediate cycle the lateral streams, and their tributaries have* 

 been again and again rejuvenated by oscillation of the land sur- 

 face, faulting and capture, and both lateral and cross streams have- 

 repeatedly deepened and widened their valleys. The Pre-Older 

 Basalt stream levels are in many cases hundrds of feet above that 

 of the neighbouring lateral streams, he.nce the use of the term- 

 *' high level lead." Nearly all the residuals north of the railway 

 from Melbourne to Drouin are conspicuous features, and many of 

 the stream deposits or ''leads" below them have been worked for 

 gold. 



To the west and north of Melbourne, however, the development 

 of residuals from the Newer Basalt lavas is in progress. The- 

 valleys of the Intermediate cycle have been occupied or flooded by 

 lava, and both confined and extensive lava fields have resulted. 

 The development of these Newer Basalt residuals was likewise- 

 characterised by three cycles corresponding to the first, second, and 

 third just mentioned, namely : — 



(3) The Intermediate cycle just considered, 



(4) The Newer Basalt cycle during which confined and extensive- 

 lava fields were formed in or above the lateral valleys of the Inter- 

 mediate cycle, and 



(5) The Post Newer Basalt cycle, at the beginning of which a 

 new system of drainage was initiated, and is beginning to develop 

 a system of lateral streams. Minor laterals are common, but a^ 

 evidencing the fact that the development of the residual is in a 

 youthful stage, it is significant that cross streams are correspond- 

 ingly rare, in other words, the Newer Basalt residuals have onir 

 at few localities been breached. 



