616 PROCEEDINGS OF SECTION J. 



three inches respectively. The tunnels are lined throughout with 

 eighteen inches of brickwork. Where the foundations are of good 

 rock the curved walls rest upon footings two feet two and a-half 

 inclies wide, at other places an invert arch is built fourteen inch 

 thick with a fall of twelve inches. A central drain twelve inches 

 by twelve inches, runs throughout the lenyth of the tunnel, the 

 bottom of which is two feet nine inches below the level of the 

 rails. A series of eight tunnels, constructed as described above, 

 occur in a distance of ten miles, the aggregate length of which is 

 two and a-half miles, the longest is under the Bulga Range, and is 

 nearly a mile in length. The George's River Bridge, twelve and 

 a-quarter miles from Sydney, is constructed for a single line of 

 i^ailway, and consists of six openings, each one hundred and fifty 

 feet in the clear, formed with four main lattice girders, each con- 

 tinuous over two piers, the aggregate length of the main girders 

 over all being nine hundred and tifty-six feet eleven inches, and 

 fifteen feet deep. The cross girders are two feet two inches deep, 

 spaced seven feet four inches centre to centre. The longitudinal 

 rail-bearers are eight inches deep. The piers and one abutment 

 consist of cast-iron cylinders braced together. The other alDutment 

 is built of masonry. The cylinders are sunk to an average depth 

 of one hundred and twenty-one feet, giving a clear headway of 

 thirty-five feet above summer level. Tlie details of this bridge 

 are similar to the bridge over the River Macquarie at Dubbo, 

 which has been already referred to. The unit stresses and the 

 deflections developed under test load prove this bridge to be similar 

 in strength and stiffness to that of the Dubbo Bridge. 



There is a large number of timber openings on this railway, 

 varying from ten feet to forty-two feet in the clear. They 

 extend over the following creeks, rivers, and low-lying country : 

 Port Hacking Creek, consisting of seven openings, each forty 

 feet in the clear ; Stanwell Creek, consisting of an arch thirty 

 feet in the span ; M'Anny's Creek, consisting of four 

 openings, twenty-six feet in the clear ; Stack Creek, con- 

 sisting of five openings, twenty-six feet in the clear ; Towradge 

 Creek, consisting of six openings, twenty-six feet in the clear ; 

 American Creek, consisting of eight openings, twenty-six feet 

 in the clear ; Mullet Creek, consisting of twenty-four openings, 

 twenty-six feet in the clear ; Macquarie Rivulet, consisting of 

 nine openings, twenty-six feet in the clear ; Lake Illawarra, 

 consisting of six openings, twenty-six feet in the clear ; also of 

 ten openings, fifteen feet in the clear ; and of one oj^ening, ten 

 feet in the clear. Flat adjoining Minumurra River, thirteen 

 openings, fifteen feet in the clear ; flat adjoining Minumurra 

 River, one hundred and twenty openings, ten feet in the clear ; 

 Minumurra River, nineteen openings, twenty-six feet in the 

 clear ; Minumurra River, two openings, fifteen feet in the clear ; 



