the
district; and that the various secondary rocks he examined in his route
through it seem to belong to the Cretaceous group. It appears not
improbable, therefore, that all the sonorous sand in the world yet
discovered is formed, like that of Eigg, of disintegrated sandstone; and
at least two-thirds of it of the disintegrated sandstone of secondary
formations, newer than the Lias. But how it should be at all sonorous,
whatever its age or origin, seems yet to be discovered. There are few
substances that appear worse suited than sand to communicate to the
atmosphere those vibratory undulations that are the producing causes of
sound: the grains, even when sonorous individually, seem, from their
inevitable contact with each other, to exist under the influence of that
simple law in acoustics which arrests the tones of the ringing glass or
struck bell, immediately as they are but touched by some foreign body,
such as the hand or finger. The one grain, ever in contact with several
other grains, is a glass or bell on which the hand always rests. And the
difficulty has been felt and acknowledged. Sir John Herschel, in
referring to the phenomenon of the _Jabel Nakous_, in his "Treatise on
Sound," in the "Encyclopaedia Metropolitana," describes it as to him
"utterly inexplicable;" and Sir David Brewster, whom I had the pleasure
of meeting in December last, assured me it was not less a puzzle to him
than to Sir John. An eastern traveller, who attributes its production
to "a reduplication of impulse setting air in vibration in a focus of
echo," means, I suppose, saying nearly the same thing as the two
philosophers, and merely conveys his meaning in a less simple style.

I have not yet procured what I expect to procure soon,--sand enough from
the musical bay at Laig to enable me to make its sonorous qualities the
subject of experiment at home. It seems doubtful whether a small
quantity set in motion on an artificial slope will serve to evolve the
phenomena which have rendered the Mountain of the Bell so famous.
Lieutenant Welsted informs us, that when his Bedouin first set the sand
in motion, there was scarce any perceptible sound heard;--it was rolling
downwards for many yards around him to the depth of a foot, ere the
music arose; and it is questionable whether the effect could be elicited
with some fifty or sixty pounds weight of the sand of Eigg, on a slope
of but at most a few feet, which it took many hundred weight of sand of