thin the line, suffer greatly from time to
time. The southern part of Spain also, and Portugal, have generally been
exposed to the same scourge simultaneously with Northern Africa. The
provinces of Malaga, Murcia, and Granada, and in Portugal the country
round Lisbon, are recorded at several periods to have been devastated by
great earthquakes. It will be seen, from Michell's account of the great
Lisbon shock, in 1755, that the first movement proceeded from the bed of
the ocean ten or fifteen leagues from the coast. So late as February 2,
1816, when Lisbon was vehemently shaken, two ships felt a shock in the
ocean west from Lisbon; one of them at the distance of 120, and the
other 262 French leagues from the coast[489]--a fact which is more
interesting, because a line drawn through the Grecian Archipelago, the
volcanic region of Southern Italy, Sicily, Southern Spain, and Portugal,
will, if prolonged westward through the ocean, strike the volcanic group
of the Azores, which may possibly therefore have a submarine connection
with the European line.

In regard to the volcanic system of Southern Europe, it may be observed,
that there is a central tract where the greatest earthquakes prevail, in
which rocks are shattered, mountains rent, the surface elevated or
depressed, and cities laid in ruins. On each side of this line of
greatest commotion there are parallel bands of country where the shocks
are less violent. At a still greater distance (as in Northern Italy, for
example, extending to the foot of the Alps), there are spaces where the
shocks are much rarer and more feeble, yet possibly of sufficient force
to cause, by continued repetition, some appreciable alteration in the
external form of the earth's crust. Beyond these limits, again, all
countries are liable to slight tremors, at distant intervals of time,
when some great crisis of subterranean movement agitates an adjoining
volcanic region; but these may be considered as mere vibrations,
propagated mechanically through the external covering of the globe, as
sounds travel almost to indefinite distances through the air. Shocks of
this kind have been felt in England, Scotland, Northern France, and
Germany--particularly during the Lisbon earthquake. But these countries
cannot, on this account, be supposed to constitute parts of the southern
volcanic region, any more than the Shetland and Orkney islands can be
considered as belonging to the Icelandic circle, because the s