a tendency to what the
French call _assaissement_ (I do not know the English term), which is,
nevertheless, resisted by the stone _en masse_; and a quantity of water
may likewise be held, not in a state of chemical combination, but in one
of close mixture with the rock. On being broken or quarried, the
_assaissement_ may take place, the particles of stone may draw closer
together, the attraction become stronger; and, on the exposure to the
air, the water, however intimately combined, will, in a process of
years, be driven off, occasioning the consolidation of the calcareous,
and the near approach of the siliceous, particles, and a consequent
gradual induration of the whole body of the stone. I offer this
supposition with all diffidence; there may be many other causes, which
cannot be developed until proper experiments have been made. It would be
interesting to ascertain the relative hardness of different specimens of
sandstone, taken from different depths in a bed, the surface of which
was exposed to the air, as of specimens exposed to the air for different
lengths of time.

J. R.

HERNE HILL, _July 25, 1836._

FOOTNOTES:

[Footnote 27: London's _Magazine of Natural History_, Vol. vii., pp.
644-5. The note was illustrated by engravings from two sketches by the
author of the Aiguille de Servoz and of the Aiguille Dru, and by a
diagram explanatory of its last sentence but one.--ED.]

[Footnote 28: "A small neat copy of a sketch carefully taken on the
spot," which, according to the editor of the magazine, accompanied this
communication, was not, however, published. See the magazine.--ED.]

[Footnote 29: Loudon's _Magazine of Natural History_, Vol. ix., No. 65,
pp. 488-90.--ED.]

[Footnote 30: The question here discussed was originally asked in the
magazine (Vol. ix., pp. 379-80) by Mr. W. Perceval Hunter with reference
to the condition of Bodiam Castle, in Sussex.--ED.]

OBSERVATIONS ON THE CAUSES WHICH OCCASION THE VARIATION OF TEMPERATURE
BETWEEN SPRING AND RIVER WATER.--BY J. R.[31]

274. The difference in temperature between river and spring water, which
gives rise to the query of your correspondent Indigena (p. 491),[32] may
be the result of many causes, the principal of which is, however,
without doubt, the interior heat of the earth. It is a well known fact,
that this heat increases in a considerable ratio as we descend, making a
difference of several degrees between the temperature of the ea