f - 
Appendix. 403 
to us of the elevation and appearance of the island, to account for 
the well characterised circus or mural precipice which surrounds the 
canal of communication or crater of eruption. 
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It does not farther appear, from the soundings, that this island is 
the summit of a cone of eruption with an open crater. Captain 
_ Swinburne found, within 20 yards on the western side, 18 fathoms 
soft bottom; and Capt. Smith found, at 100 yards, the island bear- 
ing from N.to N. W., from 60 to 64 fathoms; at 80 yards, the 
island bearing N. E., 70 to 75 fathoms; at 150 yards, the island 
bearing E., 62 fathoms, cinders: the soundings continuing the same 
to the distance of five or six miles; that is to say, varying from 60 
{o 70 and 80 fathoms, sand and small gravel. The extent of the 
action by which this island was elevated from below is uncertain. It 
is a curious fact, that the tides were higher at that period at Gibraltar 
than they were ever known to be; but the connexion of this phenom- 
enon with the elevation of submarine formations requires the evidence 
of correlative observations. 
Captain Swinburne observed the interior of the crater to be filled 
with muddy water, violently agitated, dashing up and down, and 
‘shooting hot stones and cinders into the air; and occasionally run- 
ning into the sea, over the edge of the crater, which was 
