86 Miscellaneous Circular 39, U. S. Dept. of Agriculture 
increase from year to year with the ber and cordwood, unless lost by fire 
increase in population. - or premature cutting. 
The increment of wood through Still the central fact is that we are 
growth is 6 billion cubic feet a year. using up our timber four times as fast 
Fre. 10.—This is a frame building corner post set directly in the 
soil without preservative treatment. About 15 per cent of the 
annual production of lumber and dimension material goes to re- 
place wood destroyed by decay in service 
Fig. 11.—Excesses in the use of timber in structural design no 
longer exist to the gegres that they did when this old highway 
bridge was built, but the use of accurate strength data for wood 
still offers an opportunity for saving structural timber 
Although this growth is mostly on as it grows, and the end of more than 
trees now in the cordwood class, it three centuries of abundance is now 
will have its effect eventually in ex- plainly in sight. 
tending the supplies of both saw tim-