A Treatise On The Principles And Practice Of Dock Engineering

148 DOCK ENGINEERING. indicated by its name. Owing to its great toughness it is capable of resist- ing great shocks. Logs can be obtained from 18 to 30 inches square. Bullet tree is a dark red wood said to be an excellent substitute for greenheart. It saws easily, takes a smooth finish, and is thoroughly tough and durable. The size of the logs runs up to 3 feet in quarter girth and 50* feet in length. Kakaralli, though a less known tree, is described as even surpassing greenheart in its qualities for marine situations, such as durability and resistance to the attacks of worms. It is close-grained, tough and difficult to saw, but easy to plane. It has one drawback in that it can only be obtained in small logs, 10 to 14 inches square, and rarely exceeding 40 feet in length. Jarrah is an Australian timber, resembling mahogany in colour, also recommended as a valuable substitute for greenheart. It is hard and close- grained, very liable to warp and split and full of clefts, filled with resinous matter. The fibres contain an acid having a pungent odour, said to be very efficacious against sea-worms and insects. Its extreme durability compared with other timbers is incontestible, and it is on record that it has survived the attacks of marine borers long after other woods have succumbed. On the other hand, there are some authenticated instances of its destruction by the white ant and the teredo. Karri, another Australian native, is hard, heavy, straight-grained, and tough. It is stronger than jarrah but less durable in damp situations, though when entirely immersed it is said to last well. No decisive evidence is fortlicoming as to its capacity to resist worms. Red Gum is another tree possessing the same characteristics as jarrah,. with strength and toughness in a higher degree, while its durability is rather less. Ironbark is one of the hardiest and strongest woods in existence, but it is not so durable in marine situations as the preceding varieties, being admittedly readily attacked by the teredo. In spite of this faet it is much used for piles in harbour works in New South Wales. The wood has a close,, straight grain, is very tough and heavy, and is white or yellowish in colour. Blue Gum, though an undoubtedly useful timber, is only suitable for dry and open situations, and it is depreciated by a tendency to warp and shrink under exposure to the sun. It is straw-coloured. Stringy bark is a hard, heavy, straight-grained wood, occäsionally employed for the superstructure of engineering works. This concludes the Australian series. Keyaki is a very important timber in Japan, being strong, durable, and easily worked. It is durable in situations alternately wet and dry, and is much used for piles. Deodar, supposed to be a variety of the Oedar ot Lebanon, is a wood of great stiffness, strength, hardness, and durability, well adapted for engineering purposes in India.