Most of the new edifices of the late pointed style in Scotland differ from those in England in many particulars. The Scottish churches are, as already stated, usually smaller in size, and consist of single compartments without aisles. Although frequently designed as cross churches, with choir, nave, and transepts, they are rarely finished, the choir or the choir and transepts being often the only portions carried out. The east end frequently terminates with a three-sided apse. This feature is almost entirely characteristic of the late pointed period. It undoubtedly owes its origin to the Scottish alliance and intercourse with France. But the leading and distinguishing feature of our late pointed style is the vaulting, the pointed barrel vault being almost universally employed. We have seen that a pointed barrel vault was used at Lincluden and Bothwell collegiate churches. It was, however, in the later edifices, after the middle of the fifteenth century, that that form of vault came into general use. This kind of arch was of simple construction, and was much employed in the castles of the period, being found convenient--first, because it was of easy construction; and second, because it could conveniently carry a roof composed of overlapping stones. This style of roof had the double advantage of being fireproof, and in the case of the castles, where it was often kept flat, of forming a platform from which the defenders could operate. It has already been pointed out[4] that many features of domestic architecture were at this time imported into ecclesiastical architecture, and the above feature of the pointed barrel vault carrying a stone roof is the first and most important. In carrying out this kind of vaulting in churches, several difficulties were encountered and had to be overcome. The most serious of these difficulties was the junction of the transepts, or side chapels, with the choir and nave. In the earlier Gothic churches this was managed by running the vault of the transepts or chapels into that of the nave, and forming a groin at the intersection. But the peculiarity of the late Scottish churches is that they carefully avoid all groins and intersections of arches. The junction of the vaults at the above intersections is, therefore, managed by a special contrivance, viz., by keeping the barrel vaults of the transepts or chapels quite apart from those of the central nave, the side vaults being stopped on gables carried up on arches in the line of the main side walls to receive them. The main nave vault is thus carried throughout the whole length of the central nave without a break, and where the opening into the transepts or chapels occurs, the main vault rests on an arch thrown across the side openings in the line of the main walls, and at a level below the springing of the main vault. The outer stone roofs of the transepts are also kept independent of that of the central nave, and do not mitre into it.