of the Hauran, east of the Jordan, appear to have been
active at the period when the present Jordan valley was filled with
water to such an extent as to constitute a lake two hundred miles in
length, but which has now shrunk back to within the present limits of
the Dead Sea.[3] Again, at the period when the extinct volcanoes of
Central France were in active operation, an extensive lake overspread
the tract lying to the east of the granitic plateau on which the craters
and domes are planted, now constituting the rich and fertile plain of
Clermont.

[Illustration: Map Of The World Showing Active And Extinct Volcanoes
(Large Dots)]

Such instances are too significant to allow us to doubt that water in
some form is very generally connected with volcanic operations; but it
does not follow that it was necessary to the original formation of
volcanic vents, whether linear or sporadic. If this were so, the extinct
volcanoes of the British Isles would still be active, as they are close
to the sea-margin, and no volcano would now be active which is not near
to some large sheet of water. But Jorullo, one of the great active
volcanoes of Mexico, lies no less than 120 miles from the ocean, and
Cotopaxi, in Ecuador, is nearly equally distant. Kilimanjaro, 18,881
feet high, and Kenia, in the equatorial regions of Central Africa, are
about 150 miles from the Victoria Nyanza, and a still greater distance
from the ocean; and Mount Demavend, in Persia, which rises to an
elevation of 18,464 feet near the southern shore of the Caspian Sea, a
volcanic mountain of the first magnitude, is now extinct or dormant.[4]
Such facts as these all tend to show that although water may be an
accessory of volcanic eruptions, it is not in all cases essential; and
we are obliged, therefore, to have recourse to some other theory of
volcanic action differing from that which would attribute it to the
access of water to highly heated or molten matter within the crust of
the earth.

(_b._) _Leopold von Buch on Rents and Fissures in the Earth's
Crust._--The view of Leopold von Buch, who considered that the great
lines of volcanic mountains above referred to rise along the borders of
rents, or fissures, in the earth's crust, is one which is inherently
probable, and is in keeping with observation. That the crust of the
globe is to a remarkable extent fissured and torn in all directions is a
phenomenon familiar to all field geologists. Such rents and fissures are