manner
different from that represented in the older charts. In their longest
diameter they form at their base a ridge nearly bisecting the gulf or
crater (see sections, figs. 64, 65).

On considering these facts we are naturally led to compare the smaller
and newer islands in the centre of the gulf to the modern cone of
Vesuvius, surrounded by the older semicircular escarpment of Somma, or
to liken them to the Peak of Teneriffe before described, as surrounded
by its "fosse and bastion." This idea will appear to be still more fully
confirmed when we study the soundings taken during the late
hydrographical survey. Thera, which constitutes alone more than
two-thirds of the outer circuit, presents everywhere towards the gulf,
high and steep precipices composed of rocks of volcanic origin. In all
places near the base of its cliffs, a depth of from 800 to 1000 feet of
water was found, and Lieut. Leycester informs us[610] that if the gulf,
which is six miles in diameter, could be drained, a bowl-shaped cavity
would appear with walls 2449 feet high in some places, and even on the
southwest side, where it is lowest, nowhere less than 1200 feet high;
while the Kaimenis would be seen to form in the centre a huge mountain
five and a half miles in circumference at its base, with three principal
summits (the Old, the New, and the Little Burnt Islands) rising
severally to the heights of 1251, 1629, and 1158 feet above the bottom
of the abyss. The rim of the great caldron thus exposed would be
observed to be in all parts perfect and unbroken, except at one point
where there is a deep and long chasm or channel, known by mariners as
"the northern entrance" (B, fig. 63) between Thera and Therasia, and
called by Lieut. Leycester "the door into the crater." It is no less
than 1170 feet deep, and constitutes, as will appear by the soundings
(see map), a remarkable feature in the bed of the sea. There is no
corresponding channel passing out from the gulf into the Mediterranean
at any other point in the circuit between the outer islands, the
greatest depth there ranging from 7 to 66 feet.

We may conceive, therefore, if at some former time the whole mass of
Santorin stood at a higher level by 1200 feet, that this single ravine
or narrow valley now forming "the northern entrance," was the passage by
which the sea entered a circular bay and swept out in the form of mud
and pebbles, the materials derived by denudation from wasting cliffs. In
th