The varieties of timber of this class most in use for building purposes are oak, beech, ash, elm, mahogany, teak. These, with a few others, will now be described in more or less detail, according to their importance.
Oak. - Of this timber there are several varieties found, both in this country, and also in America, Holland, and the Baltic.
The principal British varieties are the Stalk-fruited or Old English Oak (Quercus robur or Quercus pedunculata), in which the acorns have long stalks, and the leaves short stalks.
The Cluster-fruited or Bay Oak (Quercus sessiliflora), of which the acorns grow in close clusters with very short stalks, and the leaves have longer stalks, some nearly an inch long.
Durmast Oak (Quercus pubescens) has short stalks for the acorns and long stalks for the leaves, like the bay oak, but is distinguished by "the under side of the leaves being somewhat downy."l
Good oak is of a light brown or brownish-yellow colour, with a hard, firm, and glossy surface. A reddish tinge and dull surface are signs of decay. The annual rings are very narrow and regular, each having a compact and a porous layer, the pores in the latter being very small. Wide rings and large pores are signs of weakness. The medullary rays are hard and compact; where they are small and indistinct the wood is stronger.
When the timber is cut obliquely across, beautiful markings of silver grain appear, being caused by the cropping out of the large medullary rays.
Sound heart of oak is very durable in earth or water. It has been known to last 1000 years when well ventilated.
The timber is very strong, hard, and tough, warps in seasoning. It is very elastic, easily bent to curves when steamed or heated. It is not easily splintered, but is rather liable to the attacks of insects.
Young oak is tougher, more cross-grained, and harder to work than old oak.
It is generally considered that the timber from the stalk-fruited oak is superior to that from the Bay oak.
The respective characteristics of the two varieties, as given by Tredgold, Rankine, and other observers, are as follows : -
The wood of the stalk-fruited oak is lighter in colour than the other. It has a straight grain, is generally free from knots, has numerous and distinct medullary rays, and good silver grain; it is easier to work and less liable to warp than the timber of the Bay oak, and is better suited for ornamental work, for joists, rafters, and wherever stiffness and accuracy of form are required; it splits well and makes good laths.
The timber of the cluster-fruited oak is darker in colour, more flexible, tougher, heavier, and harder than that of the stalk-fruited oak; it has but few large medullary rays, so that in old buildings it has been mistaken for chestnut; it is liable to warp, and difficult to split; it is not suited for laths or ornamental purposes, but is better than the other where flexibility or resistance to shocks are required.
Mr. Britton says that dry rot was introduced into ships by using the Bay oak.
Mr. Laslett says that the timber of the sessiliflora is a little less dense and compact than that of the pedunculata, but they so much resemble each other, that "few surveyors are able to speak positively as to the identity of either."
The Durmast oak is decidedly of inferior quality.
Oak is sometimes felled in the spring for the sake of the bark (instead of being stripped in the spring and felled in the winter as described at p. 360). The tree being then full of sap, the timber it yields is not of a durable character.