152 THE SEAS 



structures, the problem still remains unsolved. How 

 urgent the need for a solution is, can be judged by the extent 

 of the damage done in San Francisco as the result of a 

 great burst of activity by the Shipworm in that district 

 between 1914 and 1920, when wooden piers and wharves 

 to the estimated value of ten million dollars were destroyed. 



Innumerable remedies and protective measures have 

 been tried with varying degrees of, but never complete, 

 success. Different woods vary with regard to the speed 

 with which they are attacked. Hard woods, such as teak 

 or oak, are attacked just as quickly as softer woods, but 

 some woods resist attack for a longer period owing to the 

 presence in them of essential oils or poisonous alkaloids. 

 Greenheart and Eucalyptus are examples. One of the 

 methods of protecting timber consists of leaving the bark 

 intact, for this often contains such protective oils. The 

 wood, however, requires very careful handling or the bark 

 is injured and the wood borers make their way through 

 the damaged places. In any case there is always the 

 danger that the animals will enter about the knots in the 

 wood. 



It is impossible here to do more than give a list of a few 

 of the more important methods of protecting timber. 

 Protective measures fall naturally into two main divisions, 

 those which protect the surface of the wood and those 

 which impregnate it with poison. Piles have been painted 

 with a great variety of substances in the hope of keeping 

 out borers, amongst them may be mentioned tar, copper 

 paints, and innumerable patent preparations. These are 

 usually efficacious while the coating remains intact which, 

 in the case of pier piles which are continually being scraped 

 by the sides of ships, is not long. Charring or " breaming " 

 of timber is another old method of protection, but is not, 

 apparently, very effective. Then there are a large number 



