134 HARBOUR CONSTRUCTION. 



Various methods have been adopted for protecting timber 

 from the ravages of these marine marauders. 



Covering with copper sheathing has been tried, but with 

 only partial success, as the worms, when young, are so small 

 that they can penetrate between the joints of the copper, and so 

 find access to the wood. It is, moreover, rather a costly expedient, 

 and liable to cause rapid decay of any submerged iron that may 

 be about the structure. 



Studding the surface of timber with large-headed iron nails, 

 driven close to each other, appears to answer fairly well. These 

 rust and form a casing of iron oxide, which repels the attacks of 

 the Teredo, etc. This is, however, also an expensive process, and 

 it somewhat reduces the strength of timber. 



Some timbers, in their natural state, resist the attacks of sea- 

 worms much better than others. This is not in any way due to 

 their texture, but to the fact that they contain poison or pungent 

 oils which are distasteful to these creatures. Of these green- 

 heart, sneezewood, and jarrah are the best, teak and oak being 

 also fairly good. 



In many situations, well-creosoted Baltic red-wood timber, 

 containing at least 10 Ibs. to 12 Ibs. of creosote per cubic foot, 

 will be found to answer fairly well. 1 



A few years ago (1889), I happened to visit Holyhead during 

 the time that some of the piles of the old harbour timber jetties 

 were being renewed. Those which were being taken out were 

 of creosoted timber, and they had been in the jetty since the 

 year 1860, or for about twenty-nine years. Some of them were 

 certainly very badly eaten, apparently entirely by Limnoriaf, 

 but the timber which remained was perfectly sound. 



As the cost of creosoted timber does not usually much exceed 

 one-third that of greenheart, it is well worth while to consider 

 whether, in positions where the worm is not very active, it may 

 not with advantage be used. This point, like many others, 

 resolves itself into a question of expediency. 



In order to arrive at a correct decision, it is necessary that 

 reliable data should be forthcoming respecting the site where it 

 is intended to use the timber; otherwise the estimated life of 

 the timber may be very wide of the mark. 



1 It is customary with French engineers, and some others, to use as much as 18 

 Ibs. or 19 Ibs. of creosote per cubic foot of timber, when such is to be used in sea- 

 works. 



