specimens of partially devitrified glass, in the possession of Mr. Stokes,
the sphaerulites are united into straight layers with even sides, parallel
to each other, and to one of the outer surfaces, exactly as in the
obsidian. These layers sometimes interbranch and form loops; but I did not
see any case of actual intersection. They form the passage from the
perfectly glassy portions, to those nearly homogeneous and stony, with only
an obscure concretionary structure. In the same specimen, also,
sphaerulites differing slightly in colour and in structure, occur embedded
close together. Considering these facts, it is some confirmation of the
view above given of the concretionary origin of the obsidian and natural
sphaerulites, to find that M. Dartigues ("Journal de Physique" tome 59 1804
pages 10, 12.), in his curious paper on this subject, attributes the
production of sphaerulites in glass, to the different ingredients obeying
their own laws of attraction and becoming aggregated. He is led to believe
that this takes place, from the difficulty in remelting sphaerulitic glass,
without the whole be first thoroughly pounded and mixed together; and
likewise from the fact, that the change takes place most readily in glass
composed of many ingredients. In confirmation of M. Dartigues' view, I may
remark, that M. Fleuriau de Bellevue (Idem tome 60 1805 page 418.) found
that the sphaerulitic portions of devitrified glass were acted on both by
nitric acid and under the blowpipe, in a different manner from the compact
paste in which they were embedded.

COMPARISON OF THE OBSIDIAN BEDS AND ALTERNATING STRATA OF ASCENSION, WITH
THOSE OF OTHER COUNTRIES.

I have been struck with much surprise, how closely the excellent
description of the obsidian rocks of Hungary, given by Beudant ("Voyage en
Hongrie" tome 1 page 330; tome 2 pages 221 and 315; tome 3 pages 369, 371,
377, 381.), and that by Humboldt, of the same formation in Mexico and Peru