162 Robert A. Kehle : 



Pie-Older iJasalt watersheds in the ease of an Ohler Basalt residual, 

 and tlie watersheds of tlie Intermediate eyele in tlie case of a Newer 

 Basalt residual. 



The tributary of a lateral stream that lias its source on the 

 contiguous residual has b en tern-ed a m.nor lateral and a stream 

 (usually a well-developed minor lateral) that has actually breached 

 a residual, a cross sti-eam. 



The probable extent of the Bass Strait lava field is commented 

 on. The gradients of lava fields are shortly referred to. The thick- 

 nesses and extent of other great lava fields are given. 



The type of erosion of the Pre-Older Basalt cycle of Western 

 Port is considered to he that characterising a mountain region. 

 Only its head-waters are represented between Mt. BuUer and 

 Flinders. The type of erosion of the Port Phillip system on 

 account of the few Older Basalt residuals exposed is problematical. 



Tie c ;nfiied lava fields merged into the ext3iisive biva fiilds in 

 the vicinity of the railway between Melbourne and Drouin. The 

 Western Port extensive lava field converged towards Flinders, and 

 passed thrt)ugh a l;ottle-neck there formed by the converging con- 

 tacts of the Arthur's Seat and Pyramid Point granitic series. 

 The extensive lava field of the Port Phillip area, is thought to have 

 been less extensive owing to the more graded state of the drainage 

 system. 



The effect on the lava gradient of bottle-necks and lava fissures 

 opening across valleys is considered. 



Deductions are made from the evidence of borings put down 

 at various localities on the area under consideration. The strata 

 passed through is tabulated and classified. The Older and Newer 

 Basalts are regarded as bench-marks of great stratigraphical and 

 physiographical importance, marking the termination or incep- 

 tion of the five cycles mentioned. 



The conditions affecting the development of a residual from a 

 confined lava field are responsible for three stages in their orderly 

 -evolution — (a) the rocks on one flank being a little more resistant 

 than the lava, one lateral is formed, (b) the rocks on one flank 

 being somewhat less resistant than the lava, while that on the other 

 ilank belongs to the least resistant class of rocks, two laterals are 

 formed, but one approaches maturity much more rapidly than 

 the other; (c) the rocks on both flanks offering comparatively 

 little resistance, two laterals of relatively equal importance are 

 formed. 



