It was not till the end of the twelfth and during the thirteenth century that the Gothic system had been fully worked out by the French architects. The arcuated principle had then been developed in a complete and logical manner, and had entirely freed itself from the heavy and unnecessary mass of the earlier Romanesque. Nothing was preserved except the lightest framework required for stability, enclosed with screens of tracery filled with stained glass. Every detail of the fully developed Gothic style was designed on the same logical principles as the leading structural features, and gave expression in its design to the function it was required to fulfil,[2] while the whole building was so ornamented as to be in complete harmony with the general idea.[3] In England the details of the perfected Gothic, especially as regards decorative features, were carried out somewhat in the same spirit as in France, but the leading elements in the general design do not seem to have been so fully understood or carried out. The adherence to wooden roofs--a common and general practice in England--alone shows the difference in the guiding principles which operated in the two countries. The wooden roof is a complete departure from the leading element of the arcuated style. It shows an inclination to fall back on the ancient trabeate or horizontal beam system, from which it had been the great object of the earlier mediæval architects to free their designs. The wooden roof ignores the leading idea of a vaulted fireproof covering, and abandons the principle of the concentration of the roof pressures on particular points, as is the case in groined vaulting. No doubt a wooden roof may be designed so as to throw a greater amount of its pressure on some points than on others, but the principle of the wooden roof is that of the tie beam and the distribution of the weight over the side walls. The actuating motive of Gothic design in the main feature of the vaulting being thus lost sight of in England, it is not surprising to find it inactive in other directions. The Romanesque element of massive walls, with small windows, is likewise partially adhered to, and in details also the guiding principle of French design is in some respects abandoned. The round form of the abacus--so universally employed in England--may be cited as a characteristic example of departure from the Gothic principle. In France the abacus of the columns is invariably shaped so as to receive each shaft or rib which it is its function to carry; whereas the round abacus adopted in England receives indiscriminately all the members which descend upon it, and their loads are often carried by shafts not having any distinct or structural relation to the members which rest on the abacus above them.