102 THK VICTORIAN NATURALIST. 



which have been wrought by river action in the head waters of 

 the Yarra and Thomson Rivers. Some years ago Mr. T. S. Hall, 

 M.A,, drew attention, in a paper entitled, " A Lome Valley " 

 (Vict. Nat., 1 900-1, xvii., p. 29), to the beheading of one stream by 

 another in the Cape Otway Ranges. Other examples "are referred 

 to in "The Geography of Victoria," by Dr. J. W. Gregory. In 

 the present paper it is desired to describe another example close 

 at hand, in the Ringwood district, where part of the Dandenong 

 Creek basin has been captured by the Mullum Mullum or Deep 

 Creek, and thus water which formerly drained into the Carrum 

 Swamp has been turned into the Yarra. 



A brief account of the physical features of the area concerned 

 will show the present stream arrangement, and enable a com- 

 parison to be made with the original stream disposition impressed 

 upon the coastal plain as it was slowly raised above sea level, 

 towards the close of the Tertiary period. The eastern and south- 

 eastern suburban area of Melbourne forms part of a fairly exten- 

 sive sandy plain rising gradually inland from the eastern shores of 

 the Bay to a height, at some ten or twelve miles inland, of about 

 500 feet above sea level. The surface for the most part, 

 where the plain has not suffered denudation too severely, consists 

 of sands, sandy clays, grits, and water worn gravels. Much of this 

 material was spread out by rivers over a platform of highly- 

 inclined Palseozoic shales and sandstones, which are well exposed 

 in many of the road and railway cuttings near Melbourne. 



Part of this deposit, however, was laid down beneath the waters 

 of a shallow sea close to an old coast line, no longer recognizable. 

 The gradual upheaval of this shallow sea margin gave rise to a 

 characteristic coastal plain with a general south-westerly inclina- 

 tion, and across its gentle slope the streams from the high lands 

 found their way to the new shore line. 



On the land side, where the uplift was greatest, the action of 

 running water has been so active that much of the mantle of this 

 comparatively soft deposit has quite disappeared, and the streams 

 have extensively incised their valleys in the underlying rock, 

 giving the characteristic undulating landscape so well known about 

 Surrey Hills, Box Hill, and Doncaster, and so unlike the original 

 plain from which this present land form has been derived. The 

 Yarra drains the northern part of the area under consideration, 

 and it has deepened its course rapidly, so that its tributaries, 

 draining from the northern part of this district, have a fairly short, 

 steep slope, and though they are intermittent streams, have, never- 

 theless, been such active denuding agents that only several 

 isolated hilltops still retain the easily recognised red grits and clays 

 of the coastal plain. 



The highest part of this region lies near Mitcham, and here the 

 fall to the Yarra is shortest and steepest. The surface features 



