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PORT JACKSON SILT BEDS. 



square miles. The ripper portion and most of the eastern flank of 

 this watershed is formed of soft shales, whilst the steep spurs and 

 broken precipitous ravines of the north and south shores and of 

 the western flank are composed of hard Hawkesbury sandstone^ 

 The shale country is intersected by numerous small watercourses, 

 harmless enough when with shallow tortuous channels they flowed 

 at the foot of gentle slopes covered with dense underwood and 

 forest trees, but now, worn into large clear channels in places over 

 20 feet wide and 6 feet deep, and receiving the immediate drainage 

 of thousands of acres of cleared and settled land, they discharge 

 immense bodies of silt into the river and harbour after every rain 

 storm. A sample of this storm water taken by me from one of these 

 channels between Ashfield and Croydon, and dried off, left a 

 residue equal to 16 grains per gallon. The discharge of the stream 

 was approximately 500,000 gallons per hour, so that it was actually 

 delivering nearly 5 J tons of matter in suspension every 12 hours 

 into the river. The largest proportion of this matter would 

 certainly have remained in suspension and been carried out to sea 

 but the heavier portion, liable to settlement, would have added 

 largely to the mud flats in the bay it entered and the river beyond. 

 The power that yet remains to the tidal currents to transport this, 

 silt is also an unknown quantity, and must remain so until after 

 careful investigation, but judging from the mud flats rising in the 

 bays and lower portion of the Parramatta River, and the depth of 

 ooze in the channels of the harbour there is good reason to fear- 

 that it is constantly decreasing. 



The next question as to the extent that the silt and drainage 

 can be prevented from entering the harbour can and should be 

 dealt with at once. During low tide a large area of the bays 

 above Darling Harbour are nothing but mud fiats, which emit a 

 most offensive stench far from conducive to the health of all 

 living in their neighbourhood. By a judicious arrangement of 

 fascine spurs or jetties, these bays might be converted from large 

 cesspools into reservoirs or warping basins of great utility, not 

 only for conserving water to supply the tidal current at low water 

 but also for receiving the drainage of the country from the water 

 courses alluded to, which together with the matter in suspension 

 brought in by the tides, would assist in gradually reclaiming them.. 

 At the same time these flats, being rarely uncovered with water, 

 would not be nearly so unpleasant to the suburbs around them,, 

 nor so prejudicial to the health of their residents. The fascine- 

 spurs should converge to small outlets, and should allow of f tide 

 to flow over them, thus they would retain water within their 

 boundaries until the return of the tide. 



By this means the alluvium from the erosion of the country and 

 the drainage of the suburbs stretching 16 miles between Sydney 



