CotKiUry Sod.l/i of Yarra. 27'J 



The valli-ys alxnit ( 'lieltcnhaiii liavc vrr-v little power to re-open 

 their chaiiiiels if liloekeJ by any eau8e. Fur example the swamp 

 east of the Culf Club House at Sandringham lies at the north- 

 west end of a Itollow below the 100 ft. contour, about 50 chains 

 long and of an area of 50 acres. The whole catchment up stream 

 from the swamp is only about 300 acres. If a barrier below the 

 swamp were only to reach 102 ft. above sea level, it would require, 

 neglecting the depth below the 100 ft. contour, tW'O feet of Avater 

 over more than 50 acres to surmount the barrier, or over 4 inches 

 of rain delivered into the hollow so rapidly that absorption could 

 be neglected. A very low barrier is evidently insurmountable in 

 such a case. The valley wotdd be re-opened by the stream cutting 

 back from the lower side of the barrier, and as the direct catch- 

 ment here is very small, the chief agent would be the oozing of 

 water along the old Ijed. If the old bed had reached impermeable 

 material this woidd be much more powerful. A stream which has 

 reached less jjermeable beds is therefore much more able to keep 

 its channel open. Wind action or tlie wash from adjacent slopes 

 might make a barrier, especially after a portion of the heath had 

 been swept by tire and the sand left unprotected. It may l3e noticed 

 that while two and a half feet to the chain can be regarded as 

 moderately steep in the tertiaries, some hillsides reach as much as 

 10 feet to the chain, and might rapidly supply much material from 

 these relatively unstable slopes. 



As has been noticed, strikes of l)eds and of joints are often 

 north-westerly in the tertiaries. Any actual inequalities of surface 

 produced l)y slight folding before emergence of these beds Avould 

 be liable to be largly or wholly levelled by marine action during 

 the elevation. Relatively Aveak parts might even be excavated, and 

 these weaker parts would probably be nearer anticlines. Hence 

 there is no probability of the production of anticlinal ridges, but 

 there is a strong probability of lines of easy excavation parallel to 

 the strike of the folds. The north-Avest and south-east valleys there- 

 fore, besides being near the direction of steepest slope from the 

 axis, are probably structurally in a strong position. The relation 

 of the unusual fold at Beaumaris to the riieltenliam axis is already 

 noticed. 



Explanation of Surface Features. 



The Brighton valleys from their simplicity and regularity are no 

 doubt the <mly system which has ever existed on this area. They <io 

 not exactly follow the present general slope, but this may have been 

 altered, either by a general depression to the south or, less likely, l)y 



