272. In addition to the fact mentioned by Mr. Hunter[30] relative to the induration of soft sandstone, I would adduce an excellent example of the same effect in the cathedral of Basle, in Switzerland. The cathedral is wholly built of a soft coarse-grained sandstone, of so deep a red as to resemble long-burned brick. The numerous and delicate ornaments and fine tracery on the exterior are in a state of excellent preservation, and present none of the moldering appearance so common in old cathedrals that are built of stone which, when quarried, was much harder than this sandstone. The pavement in the interior is composed of the same material; and, as almost every slab is a tomb, it is charged with the arms, names, and often statues in low relief, of those who lie below, delicately sculptured in the soft material. Yet, though these sculptures have been worn for ages by the feet of multitudes, they are very little injured; they still stand out in bold and distinct relief: not an illegible letter, not an untraceable ornament is to be found; and it is said, and I believe with truth, that they have now grown so hard as not to be in the least degree farther worn by the continual tread of thousands; and that the longer the stone is exposed to the air, the harder it becomes. The cathedral was built in 1019. 273. The causes of the different effects of air on stone must be numerous, and the investigation of them excessively difficult. With regard, first, to rocks _en masse_, if their structure be crystalline, or their composition argillaceous, the effect of the air will, I think, ordinarily, be found injurious. Thus, in granite, which has a kind of parallelogrammatic cleavage, water introduces itself into the fissures, and the result, in a sharp frost, will be a disintegration of the rocks _en masse_; and, if the felspar be predominant in the composition of the granite, it will be subject to a rapid decomposition. The morvine of some of the Chamouni and Allee Blanche glaciers is composed of a white granite, being chiefly composed of quartz and felspar, with a little chlorite. The sand and gravel at the edge of these glaciers appears far more the result of decomposition than attrition. All finely foliated rocks, slates, etc., are liable to injury from frost or wet weather. The road of the Simplon, on the Italian side, is in some parts dangerous in, or after, wet weather, on account of the rocks of slate continually falling from the overhanging mountains above; this, however, is mere disintegration, not decomposition. Not so with the breccias of Central Switzerland. The rock of Righi is composed of pebbles of different kinds, joined by a red argillaceous gluten. When this rock has not been exposed to the air, it is very hard: you may almost as easily break the pebbles as detach them from their matrix; but, when exposed for a few years to wind and weather, the matrix becomes soft, and the pebbles may be easily detached.