Doorways are generally pointed or trefoiled, but sometimes round-headed, and small doorways are frequently flat-headed, with the angles corbelled in the form called the square-headed trefoil, or the shouldered arch. Trefoiled arches are characteristic of this style. Arches are frequently, but not always, acutely pointed; and in the more important buildings are generally richly moulded, as in Westminster Abbey, either with or without the tooth-ornament, as the arches at York Minster. The pillars are of various forms, frequently clustered; but the most characteristic pillar of the style is the one with detached shafts, which are generally of Purbeck marble. These are frequently very long and slender and only connected with the central shaft by the capital and base, with or without one or two bands at intervals. These bands sometimes consist of rings of copper gilt, as in the choir of Worcester Cathedral, and are sometimes necessary for holding together the slender shafts of Purbeck marble. The bases generally consist of two rounds, the lowest one the largest, both frequently filleted, with a deep hollow between, placed horizontally, as at Canterbury. In pure Early English work, the upper member of the capital, called the abacus, is circular and consists, in the earlier examples, simply of two rounds, the upper one the largest, with a hollow between them; but in later examples the mouldings are frequently increased in number and filleted. Mouldings are chiefly bold rounds, with equally bold and deeply cut hollows, which produce a strong effect of light and shade. Vaults are bolder than during the Norman period and differ from succeeding styles by their greater simplicity, as at Salisbury. In the earlier examples there are ribs on the angles of the groins only; at a later period the vaulting becomes more complicated, as at Westminster. There is a longitudinal rib, and a cross rib along the ridge of the cross vaults, and frequently also an intermediate rib on the surface of the vault. The bosses are rare at first, more abundant afterwards: they are generally well worked and enriched with foliage. English vaults are sometimes of wood only, as in York Minster, and the cloisters at Lincoln. A vault is, in fact, a ceiling, having always an outer roof over it. There is a marked distinction in the construction of Gothic vaults in England and France. In England, from the earliest period, each stone is cut to fit its place; in France the stones are cut square or rather oblong, as in the walls, and only wedged out by the thickness of the mortar at the back in the joints. Fan-tracery vaulting is peculiar to England, and it begins, in principle, as early as in the cloister of Lincoln about 1220, where the vault is of wood, but the springings are of stone, and cut to fit the ribs of the wooden vault.