enabled the apse windows to be carried to a good height. Generally speaking the windows in the apse are very low, being kept down below the main arch, and admit little light, thus rendering the vault extremely dark, as, for instance, at Seton Church.
In most of the collegiate churches the barrel vaults supported a roof composed of carefully wrought flag-stones. These stones are arranged in courses, running from the eaves to the ridge, and every alternate course is higher than, and rests on, the edges of the intermediate courses. Each stone also overlaps the course which is below it in the slope of the roof. There is thus a considerable amount of cutting and fitting required, which is usually carefully executed. Sometimes each stone is hollowed in the centre, so as to carry the water away from the joints. The gutters are also wrought in stone on the same principle. Roofs of this description might evidently be made almost level, and in the case of many of the castles (as on the keep of Craigmillar Castle) that is done, and a platform for defence is thus created. In the churches, however, the stone roofs are usually pretty steep.
It is remarkable that this form of roof was a reproduction in Scotland, in the fifteenth century, of a fireproof form of construction which was much used in Provence in the eleventh and twelfth centuries. But in this country it was to all appearance an independent invention, as Provence in the fifteenth century was, architecturally speaking, very remote, and was cut off from Scotland by the intermediate styles of England and France.
It should be noted that the pointed barrel vault, although very general, was not universally employed in Scotland during the third period. One or two notable examples of well constructed groined vaults are to be found, such as the vaulting of Trinity College Church and that of "Blackader's Aisle" in Glasgow Cathedral. But these are exceptions to the general rule.
In Rosslyn College we have the finest example of the late Scottish forms of vaulting carried out to their fullest extent, together with some exceptional designs. This church differs from most of the other collegiate churches in having side aisles, and also in having groined vaults in the east end. The plan of the latter portion of the building, being copied from the arrangement at the east end of Glasgow Cathedral, has been carried out with groining, in imitation of the original; but in the other parts of the structure the vaulting conforms to that of the third pointed period in Scotland. The main central roof is covered with a continuous pointed barrel vault without a break, except an ornamental rib over each division of the bays. The soffits of each panel of the arch thus formed are carved with stars, fleur-de-lys, and other enrichments. The side aisles are also covered with a series of pointed barrel vaults. Each of these aisle vaults forms an extension of the main pier arch of the choir, carried across the aisle at
