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largest proportion of gaseous elements are the 

 destructible. 



Amongst our own trees, the chesnut and the oak, 

 are pre-eminent as to durability; and the chesnut af- 

 fords rather more carbonaceous matter than the 

 oak. 



In old Gothic buildings these woods have been 

 sometimes mistaken one for the other; but they may 

 be easily known by this circumstance, that the pores 

 in the alburnum of the oak are much larger and more 

 thickly set, and are easily distinguished; whilst the 

 pores in the chesnut require glasses to be seen dis- 

 tinctly. 



In consequence of the slow decay of the heart- 

 wood of the oak and the chesnut, these trees under 

 favourable circumstances attain an age which cannot 

 be much short of a 1000 years. 



The beech, the ash, and the sycamore, most like- 

 ly never live half as long. The duration of the apple 

 tree is not probably, much more than 200 years; but 

 the pear tree, according to Mr. Knight, lives through 

 double this period; most of our best apples are sup- 

 posed to have been introduced into Britain by a fruit- 

 erer of Henry the Eighth, and they are now in a state 

 of old age. 



The oak and chesnut decay much sooner in 3. 

 moist situation, than in a dry and sandy soil; and their 

 timber is less firm. The sap vessels in such cases are 

 more expanded, though less nourishing matter is car- 

 ried into them; and the general texture of the forma- 

 tions of wood necessarily less firm. Such wood splits 



