Lava Residuals. 151 



development of cross streams following breaching. A stream cut- 

 ting across the metamorphic zone does so in the line of least resist- 

 ance, that is, straight across it. The striking eastern prolonga- 

 tion of the Gembrook residual is a case in point. 



Y 



w 



Fig. 9. 



Configuration of actual residuals showinjj variety of form. All drawn to same scale 



and oriented. 



The section of a residual with only one lateral developed repre- 

 sents that of a bluff. The steep ascent from Cockatoo to Gembrook 

 represents the ascent of such a residual; and when the ascent has 

 been accomplished, the railway line runs along a comparatively 

 level surface at the top of the residual. The last portion of a 

 residual to succumb to erosion is usually more or less circular. 



" Uncovered residiu/ls.^' 



A physical connection between two residuals separated by the 

 valleys of cross streams may be recognised by " uncovered resi- 

 duals," or the spur or range left after the lava covering has been 

 removed. (Fig. 8.) If they are in the valley of a cross stream, 

 their general trend is towards the cross stream. An example of 

 such, which forms an important link in connecting up the valley of 

 the stream flowing from the vicinity of Mt. Buller to Flinders, is 

 the ridge (part of the Main Divide) trending south-westerly from 

 Woods' Point. The Yering Gorge described by Mr. Jutson^ has 

 probably been cut through an uncovered residual in the trail of the 

 Lilydale residual. The watershed between Dandenong and Bur- 

 wood Creeks is probably another example. There are numerous 

 typical examples to be seen in the Western Port area on the slope 

 from the Yarra watershed towards the Koo-wee-rup Swamp. 



The southern watershed of the Yarra basin and the Main Divide 

 are the only east and west trending ranges on the area under 

 consideration. They belong to tlie period when the cross streams 



1 Vide Bil.Iioff., No. 12. 



