53 



These changes, it is true, do not universally follow, for trees sometimes fall on soft 

 peat or marl beds, gradually settle into, ad are preserved for indefinite periods of time by 

 the saline antiseptics whicli are contained in them. 



Sometimes, however, when so exposed, the vegetable tissues become slowly dissolved and 

 are replaced by silico-aluminous depositions which exactly resemble them and which aie in com- 

 mon language wrongly denominated petrifactions. 



The decay before referred to is much more perceptible in trees that have bark on 

 than when it has been removed; besides, when stripped they are seldom attacked by worms 

 and borers, which, unless care be taken to prevent their action, prove energetic agents in the 

 work of vegetable decomposition. 



Timber so affected, though subsequently seasoned, is more liable to decay than that which 

 has been seasoned properly and with care before use, especially if exposed to a confined, 

 heated and moist atmosphere, such as is frequently presented in the holds of ships, particularly 

 in low latitudes. Thus exposed, decomposition recommences, and the result is one variety of 

 the dry rot or a total breaking up of the woody structure into powder. 



Timber that is perfectly sound after long exposure is also subject to this disease, that of 

 the live oak perhaps only excepted. It has been represented as the work of animalcnla, but if 

 present, they result from and are not the cause of decay in timber any more than they are 

 in dead animal substances, where they are known to abound in great numbers. 



It has also been ascribed to fungi, which no doubt are the destructive agents of wood 

 under some circumstances ; but in such, as before referred to, it arises, beyond a doubt, from 

 the entire decomposition of the adhesive substances Avhich are assimilated during the growth 

 of trees and firmly bind the fibres together. The destruction of these substances being 

 complete the organism ceases and nothing remains but the residuary powders. 



Some of the timber brought to our market will, if examined, be found to have suffered 

 from some of the diseases before described, but it generally commands as high a price as 

 that which is perfectly sound, probably because the purchaser is ignorant that any difference 

 in the quality exists ; but the carpenter who uses such timber is inexcusable ! particularly 

 in the structure and repair of ships, and merits punishment for it as much as the house- 

 breaker or incendiary. 



This subject is of great moment, taken in connection with the wants and relations of 



civilized life, but one which, I regret to say, attracts very litde attention from those who are 



most immediately interested in the durability of timber. 



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