In Spofforth Castle, two materials, a magnesian limestone and a sandstone, have been employed, the former in the decorated parts, and the latter for the ashler, and although both have been equally exposed, the magnesian limestone has remained as perfect in form as when first employed, while the sandstone has suffered considerably from the effects of decomposition. In Chepstow Castle a magnesian limestone is in fine preservation, and a red sandstone rapidly decaying. A similar result was observed in Bristol Cathedral, which afforded a curious instance of the effects of using different materials; for a yellow limestone and a red sandstone have been indiscriminately employed both for the plain and the decorated parts of the building; not only is the appearance unsightly, but the architectural effect of the edifice is also much impaired by the unequal decomposition of the two materials. After enumerating these and other examples, the Report gives the preference to the limestones, on account of their more general uniformity of tint, their comparatively homogeneous structure, and the facility and economy of their conversion to building purposes; and, of this class, preference is given to those which are most crystalline. Professor Daniell is of opinion that the nearer the magnesian limestones approach to equivalent proportions of carbonate of lime and carbonate of magnesia, the more crystalline and better they are in every respect. It was considered that this crystalline character, together with durability, as instanced in Southwell Church, &c.; uniformity in structure; facility and economy in conversion; and advantage in colour, were all comprised in the magnesian limestone, or dolomite of Bolsover[2] Moor and its neighbourhood, and was accordingly recommended as the most fit and proper material to be employed in the New Houses of Parliament.[3] This opinion was not arrived at, nor this recommendation made, until after a very extensive series of experiments had been completed by Professors Daniell and Wheatstone upon specimens of the stones of the various quarries visited by the Commissioners. The specimens, as delivered to these gentlemen, were in the form of two-inch cubes. These experiments were of a most comprehensive kind. The composition of the stones was determined by chemical analysis:--their specific gravities; their weights after having been perfectly dried by exposure in heated air for several days; then their weights after having been immersed in water for several days so as to become saturated; the object being to ascertain the absorbent powers of the stones, which was further tested by placing them in water under the exhausted receiver of an air-pump. The stones were also subjected to the process of disintegration, invented by M. Brard, the object of which is to determine, by easy experiments, whether a building-stone will or will not resist the action of frost. Lastly, the cohesive strength of each specimen, or its resistance to