and phonolite. This order of succession is repeated several times,
the occurrence of the layers of heavy hlue basalt, with embedded
crystals as before mentioned, being at altitudes of 200,
300, and 400 feet above the sea line, Until the whole Island is built
up to the crater’s edge.* While some of the lava beds are very
compact, others are more or less scoriaceous and cellular,f their elongated
almond-shaped cavities clearly indicating the direction of their
flow. In addition to this evidence, and that of the angles of inclination,
that the strata have scarcely been disturbed from their
original positions, when flowing from Sandy Bay northward, we also
find the embedded crystals of augite, one of the most brittle of
minerals, to exist in a perfect state only around the neighbourhood
of Sandy Bay. All the embedded augite, on the northern side of
the Island, has been broken into small irregular fragments, evidently
by attrition while flowing to so great a distance. Scarcely is a
complete crystal of this mineral to be found beyond the walls of the
crater, while inside the crater itself, as at Lot and other places, the
most perfect crystals exist in large numbers,
It is somewhat remarkable that, excepting the beds of hard
basalt containing embedded crystals, the lavas show a gradual tendency
to a more felspathic composition as they approach the highest
part of the Island; the most recent being also the most felspathic.
Lavas of such a character are more readily acted on by atmospheric
influences, and, being more easily reduced by disintegration into
alluvial soil, seem to indicate a thoughtful care on the part of the
Great Creator, in thus facilitating the process for forming a surface
soil to this rocky land. Still more strikingly is this illustrated by
the fact that all the uppermost layers of lava which once existed, and
have now through disintegration entirely worn away from the high
central parts of the Island, had felspar for their chief constituent.
* These Basaltic layers are seen cropping ont on Munden’s Point and Hill; they appear
also at the following places: above Chubb’s Spring House, immediately over the bridge and
little waterfall at the foot of Barnes’ Road, about half way up Barnes’ Road, at Francis Plain
and along the watercourse road, and also at Southerns, where a thick flow on the roadside is
most probably the same as that seen at Francis Plain; “ The Rock in Plantation grounds,
as well as a stratum at Arnos Vale entrance iron gates, show the same composition; while immediately
over Cat Hole there occurs a layer of greystone with only a few small widely
scattered crystals of olivine. It is not these but the pvre basaltic lavas which generally follow
on the beds of laterite.
t Towards the lower part of Barnes’ Road a layer of very cellular lava, with cavities about
the size of peas lined with very minute zeolitic crystals, occurs.
Having thus noticed the building up of the Island to the present
edge of the crater, and turning our attention to those thick, almost
horizontal, beds of lava, highly felspathic in their composition, which
appear on the eastern side of the Island, and are plainly visible at
Horse Point, we cannot resist coming to the conclusion th at the
Island was at one time very much higher as well as much longer
and broader than its present dimensions, and that these beds are the
fragmentary remains of the latest lava ejections from the crater.
We get a further sight and knowledge of these recent lavas, which
once capped the whole, by a visit to the high conical hills situated
on the south-eastern corner of the Island, called Great and Little
Stone. Top. Here, together with the broad thick layers at a lower
altitude not far distant, running round the promontory on the
eastern coast, known as Horse Point and Holdfast Tom, we see
the last remnants of a series of greystone lavas, which were the most
recent of all, and once, so to speak, crowned the whole mountain top of
this volcanic pile, but, being subsequently worn away, left it as it now
exists. Portions of these layers of lava, nine or ten in number, still
remain, in resemblance much like gigantic steps, where they reached
down to the sea at Horse Point, of quite a different formation from
the remainder of the coast. They are composed of a very finely
crystalline felspathic greystone lava, separated by beds of white
marl, produced through the decomposition of the lava itself, and
traversed by veins of pyrolusite or black oxide of manganese.
They incline seawards at an angle of one to two degrees. The
greater the altitude at which this lava exists, the more has it passed
into a sort of whitish clay or marl, thus exemplifying the facility
with which it would, by atmospheric action be removed from the
highest parts of the Island. The few fragments which still remain
on the very summits of Great and Little Stone Tops, as well as on
the loftiest portion of Horse Point itself, show plainly the influence
produced upon it by the higher regions.
I t is this formation in the eastern portion, differing so much from
other parts of the Island, which has given rise to the idea that it once
was part of a Continent. Could we glance at the Island as it stood
when volcanic action ceased, we should see its mountain peaks rising
high into the clouds, a thousand feet perhaps, or even more, above
their present altitude; the huge crater lying on one side, and on the
other sloping plains, stretching several miles further out to sea than