W., The True
Bearing Of The Latter Being S. 13 1/2.
W. Thus the magnetic fluid seemed
on this spot to have less influence on the needle, than on the spot where
its power was first observed; and at a short distance from the base of
the hill the needle regained its natural position.
The rocks, when
broken, were of a dark iron grey: they did not appear to contain any
iron, for when tried at the tent, the magnet had no power over them.
I could not discern any regular stratum of rock, the hill being covered
with large detached stones, many of which formed figures of five and six
sides: the evening was too far advanced to permit any farther
observations to be made. [Note: The island of Cannay, one of the
Hebrides, affects the needle in a nearly similar manner. A rock in it is
named The Loadstone Rock.] Observed the variation of the needle by
azimuth, to be 6. 22. E.
August 8. - We set off early this morning to ascend Mount Exmouth,
distant four or five miles: at its base we crossed a pretty stream of
water, having its source in the Mount; it took us nearly two hours of
hard labour to ascend its rugged summits: we were however amply
gratified for our trouble by the extensive prospect we had of the
surrounding country. Directing our view to the west, Mount Harris and
Mount Forster, whose elevations do not exceed from two to three hundred
feet, were distinctly seen at a distance of eighty-nine miles. These two
spots excepted, from the south to the north it was a vast level,
resembling the ocean in extent and appearance. From east-north-east to
south, the country was broken and irregular; lofty hills arising from
the midst of lesser elevations, their summits crowned with perpendicular
rocks, in every variety of shape and form that the wildest imagination
could paint. To this grand and picturesque scenery, Mount Exmouth
presented a perpendicular front of at least one thousand feet high, when
its descent became more gradual to its base in the valley beneath, its
total elevation being little less than three thousand feet. To the
north-east commencing at N. 33. E., and extending to N. 51. E., a lofty
and magnificent range of hills was seen lifting their blue heads above
the
horizon. This range was honoured with the name of the Earl of Hardwicke,
and was distant on a medium from one hundred to one hundred and twenty
miles: its highest elevations were named respectively Mount Apsley, and
Mount Shirley. The country between Mount Exmouth and this bounding range
was broken into rugged hills, and apparently deep valleys, and several
minor ranges of hills also appeared. The high lands from the east and
south-east gradually lessened to the north-west, when they were lost in
the immense levels, which bound the interior abyss of this singular
country; the gulf in which both water and mountain seem to be as
nothing. Mount Exmouth seems principally composed of iron-stone; and
some of the richest ore I had yet seen was found upon it. On its sides
were many different stones; but its perpendicular cliffs were of a dark
bluish grey colour, shining when broken, very heavy, and close grained.
Mount Harris, and Mount Exmouth, are composed of distinct materials, and
in their formation bear not the slightest resemblance to each other;
the granite of the former being more allied to the hills to the
south-south-east of it, from which however it is distant at least one
hundred miles, a perfect level filling up the intermediate space. Many
new, and otherwise interesting subjects of the indigenous botany were
discovered on the hills: among which were a species of persoonia, not
previously observed, some xanthorrhaeae or grass trees, and two or three
coast plants. The heteromorphous sterculia of the interior, and some
species of eucalyptus of very stunted growth covered its sides, which
however for a considerable distance were not deficient in grass.
Sandstone
was found in large masses in the rivulet at its base, with pebbles of
various colours, and of species none of which was found on the mount
itself. It was near four o'clock before we returned to the tent, highly
gratified with our excursion.
August 9. - In the course of the day, I again ascended Loadstone Hill,
and repeated the experiments made on Friday, with the same results.
Several different stations on the summit were tried, and the needle was
variously affected; the spot where the phenomenon was first observed
seemed to have the greatest effect on the needle. A common sewing needle
was strongly rubbed with a magnet, and balanced on the point of the
rock, when it was much agitated, and the point flew round from the
north to the south. The needle of the circumferenter, taken out of the
box, was affected in a similar manner, only that when balanced on the
rock, the fluid did not possess sufficient power to turn the point more
than one point of the circle instead of quite round, as when balanced in
the compass box. A compound magnet was laid on the rock, and applied to
it in different ways, but it did not seem in any manner affected by the
power which had so surprised us with its effect on the compass. The
weather within the last week has become perceptibly warmer: the
thermometer being seldom under 70 degrees at noon. The fires of the
natives were seen at no great distance from us; and they seem to attend
upon our motions pretty closely. The observations made here placed us in
lat. 31. 13. S., long. 148. 41. 30. E., and I estimate the mean variation
to be about 7 1/2 easterly. We found that no reliance could be placed on
bearings taken with the compass on heights in this vicinity, and I am
fearful that the bearings taken from Mount Exmouth will require
verification, a difference of 4 degrees being observed in some, when
compared with other bearings, which could not be supposed to be affected
by the magnetic fluid.
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