Timber is generally divided into 2 classes, called " pine " woods and "hard" woods. The chief practical bearings of this classification are as follows: - Pine wood (coniferous timber) in most cases contains turpentine; is distinguished by straight-ness of fibre and regularity in the figure of the trees, qualities favourable to its use in carpentry, especially where long pieces are required to bear either a direct pull or a transverse load, or for purposes of planking; the lateral adhesion of the fibres is small, so that it is much more easily shorn and split along the grain than hard wood, and is therefore less fitted to resist thrust or shearing stress, or any kind of stress that does not act along the fibres. In hard wood (non-coniferous timber) is no turpentine; the degree of distinctness with which the structure is seen depends upon the difference of texture of several parts of the wood, such difference tending to produce unequal shrinking in drying; consequently those kinds of timber in which the medullary rays and the annual rings are distinctly marked are more liable to warp than those in which the texture is more uniform; but the former kinds are, on the whole, more flexible, and in many cases very tough and strong, which qualities make them suitable for structures that have to bear shocks.

For many practical purposes timber may be divided into two classes: - (a) soft wood, including firs, pines, spruce, larch, and all cone-bearing trees; (b) hard wood, including oak, beech, ash, elm, mahogany, etc. Carpenters generally give the name "fir" to all red and yellow timber from the Baltic, "pine" to similar timber from America, and "spruce" to all white wood from either place.