_Flying Buttresses_ at this period became prominent features in large buildings. They are arches springing from the wall buttresses to the walls, and they carry off the weight and consequent “thrust” of the roof, over the central space, obliquely down to the external buttress, and so down to the ground. The _Roof_ was formed of timber, and was covered with the material most easily procurable in the district. A thatch of straw or reeds was probably the most common; shingles were procured where oak was plentiful, and slabs of stone and slate or tiles where they were obtainable. Lead was generally used only on very important buildings. Spires were also often constructed of timber, and where the framework has become warped and twisted by the weather, we have a grotesque appearance, as in the twisted spire of Chesterfield. [Illustration: PLATE 34. (Fig. 1): Simple lancet window. (Fig. 2): A triple-lancet window from Warmington, in Northants (about A.D. 1230). The lights are placed under an arch or dripstone with the “eye” solid. (Fig. 3): A window of two lights, with a quatrefoil of plate tracery in the head, and a dripstone, terminated by the characteristic ornament called a “mask” or a “buckle,” from Charlton-on-Otmoor, Oxfordshire (about A.D. 1240). (Fig. 4): Five lancet windows under one arch, with the spandrils pierced, forming what are called the “eyes” of the window, from Irthlingborough, Northants (about A.D. 1280). (Fig. 5): Early English vault, groined, with moulded ribs on the groins only, from Salisbury Cathedral (about A.D. 1240). (Fig. 6): Pointed arch in the porch, from Barnack, Northants (about A.D. 1250). (Fig. 7): A trefoil-arched doorway. (Fig. 8): Characteristic Early English moulding (in section). (Fig. 9): “Dog-tooth” ornament in profile, showing how the name probably arose. (Fig. 10): A transitional tower and spire, from St. Denis, Sleaford, Lincolnshire. It shows a band of interlaced, round-headed arches, while in the belfry light it exhibits the pointed arch. The four corners are filled up with half-pyramids inclining from the angles. This angle-pyramid, which marks the transition from the square form of the tower to the pointed form of the spire, is known as the _broach_, and the “broach-spire” is quite the characteristic form assumed by the early stone spires in England. (Fig. 11): “Dog-tooth” ornament, front view. (Fig. 12): Door with “shouldered” arch, from Lutton, Huntingdonshire (about A.D. 1200).] [Illustration: PLATE. 35.