MATERIALS. 137 



Jarrah. The quality of this timber is much influenced by 

 the nature of the soil upon which it is grown. The best, and 

 only kind serviceable for sea-works, is that obtained from the 

 summit of the granite and ironstone ranges south of Perth, in 

 Western Australia. That grown upon the sand-flats in the same 

 district is of inferior quality. 



The best jarrah effectually resists the attack of sea-worms, 

 and may be obtained in logs of large size, viz. from 40 feet to 

 45 feet in length, and up to 24 inches square. Round masts 

 may be obtained measuring from 50 feet to 60 feet in length, 

 and from 3 feet to 4 feet diameter at the large end, tapering to 

 12 inches or 18 inches diameter at the smaller end. 



In ordering Jarrah, special care should be taken to ensure 

 only the best description being supplied. In appearance, the 

 good and bad qualities vary but little, and cases of failure have 

 occurred where timber grown on the sand-flats has inadvertently 

 been used. 



A serious objection to this wood is its extreme liability to 

 split, not only by exposure, but also while being driven as piles. 

 In driving piles, it is necessary to hoop them in the same 

 manner as greenheart. 



This tendency to split is, however, much more pronounced 

 than in greenheart, and, notwithstanding all the precautions 

 which may be taken, piles often split so badly as to necessitate 

 their being drawn and cast aside. 



In driving piles of this timber, or of greenheart, a ram 

 weighing not less than 25 cwt. should be used, and a short fall 

 say 3 feet to 4 feet should be given. 



In jarrah, decay usually commences at the heart. 



American Rock Elm is very tough, and is chiefly used for 

 "fendering." It is durable in water if not attacked by sea- 

 worms, which it cannot resist. 



Black Ironwood has been extensively used in sea- works in 

 Cape Colony. 



It is very hard, tough, and heavy, and possesses great strength. 

 Notwithstanding these qualities the Teredo eats it freely, and 

 out of water it is liable to decay somewhat rapidly. It is not, 

 therefore, a very suitable wood for sea- works. 



It may be obtained without difficulty in logs of from 12 

 inches to 14 inches square, and up to 35 feet or 40 feet in length. 



Sneezewood is as strong and as hard as black ironwood, and 



