e of which leucite occurs, generally as
the most abundant mineral, always as an essential constituent. On the
other hand, the composition of the lavas of Etna, determined by
Professor A. von Lasaulx, from specimens taken from the oldest
(voraetnaeischen) sheets of lava down to those of the present day,
indicates a rock of remarkable uniformity of composition, in which the
components are plagioclase felspar, augite, olivine, magnetite, and
sometimes apatite; but of leucite we have no trace.[9] In fact, the
lavas of Etna are very much the same in composition as the ordinary
basalts of the British Isles, while those of Vesuvius are of a different
type. This seems to suggest an origin of the two sets of lavas from a
different deep-seated magma; the presence of leucite in such large
quantity requiring a magma in which soda is in excess, as compared with
that from which the lavas of Etna have been derived.[10]

[1] _Memoires pour Servir_, etc., vol. ii.

[2] Daubeny, _Volcanoes_, p. 270.

[3] Von Waltershausen, _Der Aetna_, edited by A. von Lasaulx.

[4] Lyell, _Principles of Geology_, vol. ii., edition 1872.

[5] Its height, as determined by Captain Smyth in 1875
trigonometrically, was 10,874 feet, and afterwards by Sir J. Herschel
barometrically, 10,872 feet.

[6] _Atlas des Aetna_ (Weimar, 1858), in which the different lava-streams
of 1688, 1802, 1809, 1811, 1819, 1824, and 1838 are delineated.

[7] Sir William Hamilton observes that history is silent regarding the
first eruptions of Etna. It was in activity before the Trojan War, and
even before the arrival of the "Sizilien" settlers. Diodorus and
Thucydides notice the earliest recorded eruptions, those from 772 to 388
B.C., during which time the mountain was thrice in eruption. Later
eruptions took place in the year 140, 135, 125, 122 B.C. In the year 44
B.C., in the reign of Julius Caesar, there was a very violent outburst of
volcanic activity.--_Neuere Beobachtungen ueber die Vulkane Italiens und
am Rhein_, p. 173, Frankfurt (1784).

[8] "Report on the Chemical and Mineralogical Characters of the Lavas of
Vesuvius from 1631 to 1868," _Transactions of the Royal Irish Academy_,
vol. xxvi. (1876). In the lava of 1848 leucite was found to reach 44.9
per cent. of the whole mass. In that of Granatello, 1631, it reaches its
lowest proportion--viz., 3.37 per cent.

[9] A. von Lasaulx, in Von Waltershausen's _Der Aetna_, Book II., x. 423.

[10] The view of Professor