41 
trees having large leaf areas and growing in open woods, as second- 
growth timber. 
Change of sap-wood to heart-wood. — In large trees this change takes 
place in from ten to fifteen years, while in younger trees, growing in 
the New England States, the change is completed sooner, usually m 
four to six years. This is important, as the majority of ties are cut 
from small timber, and flattened only on t wo sides, the sap wood form- 
ing but small portions of the faces of the ties. 
Durability of Chestnut ties. — Chestnut wood is far more durable in 
contact with the soil than any other species considered in this paper, 
except, possibly, the White Cedar. But as soon as iron comes in con- 
tact with the longitudinally arranged fibers of the unseasoned wood, 
its durability is decreased, and decay is likely to commence, especially 
around the spikes. After a few years ties of sound Chestnut are found 
to decay from the surface downward, and rapidly in the vicinity of the 
spikes and under the rails. In most soils, if the ties remain in the track 
over six or eight years, the ends and central portions above the ground 
become affected, while the portions under the ballast are sound. The 
order of decay is the reverse of that of White Oak, YelknvPine, and 
Hemlock, and the body of the ties lasts longest when fully imbedded 
in the ballast. 
Chestnut is a soft wood, and in ties which have been removed from 
the track after four to six years' service, on account of cutting under 
the rails and injuries from spiking, the ends and centers are found so 
sound that the opinion has been quite general that Chestnut ties do 
not decay under ordinary service, but that the failure is due to the 
mechanical destruction of the wood-layers under the rails. After hav- 
ing the opportunity during the past two years of examining many 
thousand Chestnut ties, removed from the tracks, I find this opinion 
needs important modification. Cut out a section of a tie which has had 
four years of service under fair traffic, and incipient decay is found to 
have commenced in all of the layers which have been loosened, except 
three or four under and next to the rail, as here the air dries the wood 
too rapidly for fermentation to be set up at once; but the fermenta- 
tion which takes place under these layers soon renders the fibers soft 
and brittle and capable of furnishing but little support to the rails. 
It is a well-known fact that the rapidity of abrasion increases with the 
age of service, which would be expected after an investigation. Could 
we find ties where the injury to the wood-fibers from the spiking did 
not show, the affected spot would be V-shaped, the included angle be- 
ing larger for a broad- than for a narrow-faced tie. This effect can be 
noticed in Figure 1 (page 61), though that of the spike is included on 
one side, the dark portion representing the injury. In Fig. 2 the in- 
jury is shown extending from the spike along the fibers. In Chestnut 
ties the spikes soon discolor the wood in immediate contact, and after 
this has taken place fermentation is more easily set up in the discolored 
