DISCUSSION. 153 



foundations as is the case with brick arches. From the above 

 example I do not think there can be any question as to the great 

 commercial and economical advantages of timber for this particular 

 class of viaduct. Professor Kernot of the Melbourne University 

 informed me in a letter dated 18th February 1889, that in Gipps- 

 land Victoria, timber viaducts of 15 feet spans and a height of 

 from 8 to 10 feet above ground had been erected at an average 

 cost of less than £2 per foot of length for single line. With 

 reference to the American deck constructed of Australian hard 

 wood, a considerable number of bridges have been fitted with this 

 class of deck on the New South Wales Railways, and from my 

 observations I am of opinion that for most classes of bridges it 

 possesses advantages over all other descriptions of decks that have 

 been brought forward, for the following reasons : — Firstly — It 

 makes a very easy road to run over and in the case of iron bridges 

 greatly reduces the impact and jar on the iron work. Secondly — 

 In case of a derailment there is no possibility of a train going 

 through the deck, and the guard timbers would most probably 

 prevent the vehicle going over the side. Thirdly — It is practically 

 tire-proof. Fourth — As the sleepers are only 16 inch centres 

 there is practically a continuous bearing for the rail, and there is 

 therefore no risk of the rails breaking on the bridge, and if a 

 breakage should occur the rail would not be easily misplaced. I 

 notice in Professor Warren's paper that planks are shewn down 

 the centre of the deck of his proposed bridges, I think this must 

 have been an oversight, as they are not required, and would be 

 liable to cause fire. In conclusion it is to be hoped that consider- 

 ing the great value of our timbers, the question of the conservation 

 and planting may be energetically taken in hand by the Depart- 

 ment of Forests, so that our children may not be able to say that 

 we came into a heritage of the finest timber for engineering works 

 known, and after using a small portion of it ring-barked and 

 wasted the rest, and were too short sighted and selfish to take 

 the necessary steps for the conservation of this most valuable pro- 

 duction of the soil 



J. F. Mann — The points under discussion refer to the durability 

 and inflammability of ironbark timber for bridge flooring in com- 

 parison with pine timber. It has been shown that the advantage 

 of the former over the latter as to durability is as twenty-five 

 years to eight, and I desire to point out that this period could 

 be extended by using split slabs, whereby the grain or fibre of the 

 wood would be retained intact throughout the whole length of 

 the piece, in preference to sawn stuff ; and I further wish to 

 point out that, when dry, ironbark timber is most inflammable, 

 certainly not to the extent of pine, but still liable to catch fire, as 

 when once alight the fire will smoulder throughout the whole 



