Properties in Nature is it owing that the Stones in Buildings,
formed originally of the frailest Materials, gradually become indurated
by Exposure to the Atmosphere and by Age, and stand the Wear and Tear of
Time and Weather every bit as well, in some instances much better, than
the hardest and most compact Limestones and Granite?_[29]

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