cm 



So mucli of the wood work, in all tliese construotions, 

 as may be exposed to the air, and, particularly, such 

 parts as are subject to the alternate action of the air and 

 water, are liable to more or less rapid decay, and should 

 be protected by thick coatings of paint, or other preser- 

 vative material. Such other parts as are imbedded in the 

 embankment, however, will be found to last for years. 



