PART I I .— GEOLOGY AND MINERALOGY.
T he map of the Island shows it to be a most irregular-shaped piece
of land, with an extreme length from East to West of ten and a
quarter miles, an extreme width from North to South of eight and
a quarter miles, and having several small islets dotted here and
there around its jagged coast. A high central ridge, varying in
altitude from two thousand to nearly three thousand feet, commences
on the south-eastern side of the Island, and, taking a
semicircular course towards the south-western side, separates the
Island into two portions; that portion to the south of the ridge
takes the form of a huge bowl with its edge partly broken away,
now known as Sandy Bay; while th at on the East, North, and West,
slopes gradually away, at angles varying from 8° to 10°, towards the
sea, terminating at the coast line in perpendicular cliffs from 450
to 2000 feet in height. This great wall of rock, which, on approaching
the Island from all but a southerly direction, seems to
defy an entrance, is intersected by a number of deep and narrow
gorges running at right angles from the coast line towards the
central ridge, where they lessen considerably in depth and width.
The only town is situated in one of these gorges on the north side
of the Islan d ; it being one of the largest, may, probably, in some
measure, account for its selection as a site for the first settlement.
In size they vary considerably, and in some places lie close together,
separated only by a narrow ridge several feet in width, while m
others they are more than a mile apart.
The soundings, which are of much value in computing the
original line of coast, are quoted from a chart by Mr. George Thoms,
of H.M.S. Northumberland, under the command of Rear-Admiral Sir
George Cockburn, in the year 1815 ; they show th at the sea bottom
slopes gradually to depths of 60 or 70 fathoms at a distance
of about a mile and a half from the present coast, but immediately
beyond that there appears to be no bottom recorded at a depth of,
in some places, as much as 250 fathoms. I t will be quite necessary