146 Robert A. Kehle : 



cave and convex sides. The cutting back of a minor lateral is 

 materially assisted by the talus boulders, which accumulate in the 

 .slightest runnel and particularly on the step or fiat at the edge of 

 the lava. This step or flat is a noticeable feature near all resi- 

 duals, and is due to the gouging etJect of the heaviei- talus boulders. 

 The valleys crossing the Gippsland Road between Wilson's Quarry 

 at Berwick and the Narre Warren Creek have all been carved out 

 by minor laterals. They are due to a concave bend caused by the 

 severance some distance from the main infilled valley of a tribu- 

 tary lava field trending west of Harkaway. The old Elizabeth 

 Street Creek, Melbourne, was a minor lateral; it was formed after 

 the Older Basalt was eroded from the vicinity of its basin, and had 

 its source in the concave side of the Melbourne residual. The upper 

 valley of the Ararat Creek at Upper Pakenham bears a similar 

 relation to the eastern lateral (now captured) of the Upper Paken- 

 bam residual. 



Besides being important factors in breaching a residual, minor 

 laterals tend to throw^ light on the sinuosities of the Pre-Older 

 Basalt valleys. The minor laterals in the vicinity of Melbourne 

 seem to indicate that the Melbourne residual occupies a valley 

 which changes its direction in tli^e vicinity of Melbourne from 

 south-east to south-west. 



Process of breach i 71 ff. Cross streams. 



It is a seeming paradox that the more graded a lateral stream 

 b)ecomes the more remote is its chance of degrading a residual by 

 lateral planation. The potent factors in reducing and breaching 

 & residual are minor laterals which, cutting back on either side of 

 a bend of a residual, attack it at points in close proximity. This 

 is the prelude to the more drastic action of undergiound water, 

 which is tapped when the head of the minor lateral saps its way 

 \inder the reservoir represented by the porous beds of the old in- 

 iilled valley. The breach, then, is accomplished by sapping due, 

 in the first case, to the effect of meteoric waters, but subsequently 

 to the combined action of botli the meteoric and underground 

 waters, aided, from time to time, by the rejuvenation of the 

 laterals. The minor laterals on the east side of the Upper Paken- 

 ham residual afford examples of the combined action of meteoric 

 ^nd underground waters. Millane's, Copeland's, Moyle's, Taylor's 

 sind other springs all give rise to minor laterals, and it is a notice- 

 sible feature that landslips are conspicuous near these springs. 



