On the opposite page are illustrations showing the modifications that took place in the evolution of church architecture from the 12th to the 15th century. The triforium in the Norman period was fundamental, but in the Perpendicular period this feature was absent. The change of style may also be observed in the windows of each bay, from the simple Norman one (fig. 1) to the vertical mullioned 15th century window, figs. 4 and 8. [Illustration: THE TRIFORIUM & CLEARSTORY. Plate 14. ] [Illustration: NORMAN DETAILS. Plate 15. ] NORMAN DETAILS. Norman architecture was distinguished by the use of the traditional semi-circular arch, superseded by the pointed arch of the early Gothic period. These semi-circular arches in the earlier dates were decorated with rudely executed carvings, cut or worked with the axe. Later Norman work is very rich, the mouldings being well carved with enrichments of the Chevron, the Cable Pallet, Star, Fret or Key Patterns; the lozenge and the beading or pearling. Characteristic features of this period also are the beak-head (fig. 5) and the corbel-table, which was a series of heads of men or animals, from which spring small arches supporting the parapet. Many rich examples of Norman surface ornament are still extant; at Christchurch, Hants, a beautiful intersecting arcading of semi-circular arches occurs, the enrichment above being a scale or imbricated pattern; at St. Peter’s, Northampton, a very rich example of surface ornamentation may be seen (fig 6). Floral forms are but rarely used in Norman ornament; instances are known of the use of the rose and the fir-apple, but they are the exception and not the rule. Early doorways usually have a square head recessed under semi-circular arch mouldings, decorated with the Chevron, Key, or Beak-head. The semi-circular Tympanum over the door was plain or enriched with rude sculpture in low relief. Later doors show a great profusion of ornament in the archivolt and arch mouldings, which are often carried down the jamb mouldings. The recessed columns are also enriched with the Chevron, or diagonal lines of pearling (fig. 1), and have sculptured capitals showing a classical tendency in the arrangement of acanthus foliage and the volute. Fine examples of this period may be seen in the west front of Lincoln Cathedral (fig. 1), the Galilee porch at Durham, and the west door of Iffley Church, Oxfordshire. The Norman capitals are usually cushion-shaped, with a square abacus, enriched with the Chevron, star pattern, or the anthemion (fig. 9). The capital itself was decorated with the anthemion, or with rude volutes or segments of circles.