Sketch
Of the
GEOLOGY OF JASINGA
The report, that Mr. Horner had,
early in 1836, discovered Granite
in the rivers Chimadur
and Chiara, on the south
coast of bantam, suggested the idea, that the rock might also exist among the
defiles of the mountains, south of Jasinga, not withstanding that the Gunung Kendeng
intervenes and rises to the height of at least 5000 feet above the sea.
A rather doubtful and partially
decomposed speciment, picked up in Desember in the Chiberrum, at the western base of the gunung gede,
helped to strengthen this opinion and a profusion of boulders, observed in the
month of February following in the Chimanganteung, which flows along the southern side of the same
mountain, seemed to confirm the fact.
It was however the 16th of July
before the weather and other circumstances admitted of any regular search for
the situs of the granite.
It had been previously observed,
that the blocks, from which all former specimens had been struck, decreasein
size in proportion to their distance from the gede. It was therefore determine
to commence a search from the Kampong Chisusu, at the S.W. corner of that
mountain, and to trace the river Chimangeunteung upward to the mouth of the Chiserua,
the larges rill, that pours down from the precipitous sides of the gede.
The Chimangeunteung rises at the
S.E. foot of the gede, where it is mountain locked on all sides, except the
deep and narrow defile, through which it winds its way, between the southern
base of the gede and Gunung Limbung, an inferior range due south.
Proceeding upward, the Chirempag
is the first streamlet worth mentioning, that is met with, coming from the
gede. From Chisusu to this stream the bed of the river is formed mostly of a
black schistose rock, which in the first instance dips towards the gede, or
appears sometimes to stand on end (as at the small cascade of masigit) and
latterly dips from or rises towards it. This rock contain a small portion of
lime, as it slightly effervesces with
nitric-acid. At the spot , whre this change of inclination takes place, a
stratum of above 12 feet thick of a white, soft, earthly rock protrudes itself
between the black schist and occupies both sides of the river; the two rocks
are merely in simple contact, without any adhering or welding. On this part of
the river no other rock appear in situ; but the bed is strewed with a profusion
of blocks of trachytes, of sedementary rocks,of conglomerates, of immense
masses of scoriae, of many ton weight; some of which stand 12 or 15 feet high
and contain in their crevices aggregations of rock crystal and of plenty of
granite. Of the last stone the larges block observed was an oblong slab of
about 10 feet long, 5 feet broad and 2 feet thick. It was among this that a
cube of 2 feet of granite was found, cut through in the middle by a seam of
very compact trachyte, about 8 inches. Thick, so that the granite on it side
was entirely separated; still the whole adhered most perfectly and form one
solid block. This streaks cross both stones in the same continuous and
uninterrupted line, as it were lines of fracture, that had gaped and closed to
again; as the rock now shows no disposition to break in that direction.
From Chisusu to the mouth of the
Chirempag is about a mile in a straigh line, and from this to the Chiserua a
little les than ½ mile. On passing the Chirempag, all
trace of the granite was immediately lost, and every attention failed to
discover a single bit of it, which led to the supposition, taht its course must
be down that stream; as it is nowhere
visible on the sides of the Limbung , along which a small road winds and which
had previously been examined.
Continuing up the Chimangeunteung,
the volcanic rocks are found in situ and present a variety of position in their
dip and beds; the river has in some places worn its way into them to the depth
of several feet; whilst at others, where the texture is more compact, it is
still forced to cascade over their rugged surfaces. The black schist and white
earthy rock, mentioned in the early part of this account, again suddenly
appear, standing together nearly on their ends between the Trachyte beds, with
which they almost form a right angle, as if they had stood in their present
upright position before the volcanic matter had been poured out againts them ;
they are respectively of the thickness of 10 and 6 feet.
The bed of the Chiserua is cut
out of the former black schist; as also a more decided lime-stone, which is
however quite black. This rill is a mere ravine, worn out of the slope of the
gede and presents little interest and no variety ; the granite certainlydoes
not exist here ; the water dissapears sooner than most mountain streams and
about half way up the gede a wall of perpendicular and impassable rocks rises
up to the heiht of 30 feet. Crossing the mountain ridge at this elevation and
proceeding Westwards, the Chirempag is met with at about 800 feet above, where it falls into the
Chimangeunteung and 1000 feet below the summit of the gede. This is very
interesting little stream ; the rocks standing out boldly in all directions, of
which the principal are sedementary. At the highest point reached these rocks
seem to have undergone a general decay in situ and though they present to the
eye every appearance of a solid mass, the hammer, instead of knocking off a
fragrament, sinks into a stiff yellow clay. Lower down, where here and there
the volcanic rock thrust them-selves out to day, all sympton of decomposition
again desappears ; as if the contact had imparted a durability, which the
others do not posses. In one place a vein of trachyte is observed inserted in a
mass of sedementary rock, in the same manner as that of the Granite above
mentioned; in this case however the igneous rock has imparted a darker color
and greater hardness to its immediate neighboorhood, than what is presented by
the same rock, at a little distance, in another spot, what appears to be a fine
and close grained Granite, it seen ; but as the igneous rocks and particularly
the syenitic are known to assume accasionally the appearance of one another,
according to the condition, under which they are produced, the position seems
rather to favor the idea of its being merely a variety of thachyte. The
sedementary rocks are sometimes seem horizontal, then again perpendicular, or
inclined at some angle to the horizon ; as if the volcanic matter from below
had so disposed them, after breaking up their original continuous crust. The
Chirempag next falls into into a wide chasm of the rocks and, after running
about 400 feet under ground, again flows out further down. Below this, the
ordinary boulders or syenitic Granite again made their appearance for the first
time in this stream; they were blocks of about 4 feet square and lying more
than 100 feet above the bed of the Chimangeunteung.
The original situs of the Granite
has thus not been discovered ; wherever that spot may be, yet it cannot be far
distant. The blocks of all the Granites met with do not bear evidence of having
been much rolled, certainly not more than the other igneous rocks, with which
they are associated. The fact of the boulders increasing, both in number and
size, as we approach the Chirempag, as also their totalabsence above its mouth,
seems to point out that ravine with its mountain torrent as the path, along
which its fragments have been conveyed. The head of the Chibereum, in which the
first speciment was discovered, is only separated by a narrow ridge from that
of the Chirempag, and though the former river contains very few of these
stones, yet the fact helps to confirm the where about of the Granite; as
neither the Chikeam, which flows from the North of the Gede, nor the Chidurian,
which sweeps round its Eastern base, countains a single vestige of this stone.
The Granite inside may be higher up the Chirempag than what has been examine;
it may be concealed by the earth and dense forests; of the fragments, which we
now behold, may have been thrown down at the period of the paroxysmal explosion
of the Gunung Gede, which has evidently been much bulkier at a former period
and which now only the ruins remain.
During the period, that the
Gunung Gede of Jasinga was an active volcano, it appears probable, that the sea
washed at least its base, if it did not entirely cover it. The volcanic liquid
seems mostly to have flowed towards the South and West, and land side, where
the trachytes are still found pilled up; if any discharge took place towards
the North, it is entirely covered over by later formations; the round and
isolated hill Gunung Angsana, about five miles North from the Gede, being the
only spot, where the volcanic rocks are found in situ. That the sand and other
light tufaceous matter, ejected from the crater, have fallen into water, and by
it is been distributed, is proved by the regular strata, in which they are
still observeed, though no longer in a horizontal position, having been broken
up and displaced by their subsequent elevation. Some of the lower beds of these
volcanic ashes, resting upon limestone, contain a number ofsea shells. The
limestone itself abounds with similar productions and again reposes upon more
ancient and black, submarine and tufaceous formation; numerous sea shells, as
oysters and cockles being plentiful throughout.
In these lower black strata, near
Kampong Munchang, were discovered two tusks appearing to belong to some animal
of the genus Sue, but too fine for any of the swine tribe, now existing in the
forests. Unfortunately they were in a very brittle state and almost crumbled in
the hand; the enamel was still perfect, showing no marks of abrasion from
water; so that they cannot have travelled far; proving, that at the early
period some habitable land existed in the neighboorhood, as is further confirmed
by the numerous impressions of leaves and carbonized wood, which some strata
afford.
The strata of the different tuffs
and lime are not conformable; that is, the different beds are not exactly
parallel to each other, from which we may infer, that their elevation was not
simultaneous ; but that the risingsand deposits were alternate and successive ;
long periods of tranquility sometimes intervening, during which the limestone
was formed. The commencement of the latter is plainly seen, where the black
strata have been partially denuded ; it is at first mixed with the subjacent
black matter and by degrees becomes purer as it ascends, whereas its upper
surface terminates abruptly and hears what rests upon it, without any
intermixture.
Limestone is one of the most
common minerals found in this part of the country ; it abounds in every part of
the lower lands, as well as on the flanks of the mountains. The Gede it self
must have originally burst its way, not only through masses of Granite and
sedementary rocks, as the seems or veins, they contain of trachyte, prove; but
also have borne up with it large beds of limestone, as in the case of the
Chiserua, which is shut up in an elevated mountain defile, precluding the idea
of its having been formed there since the existence of the Gede. The highes
point, ot which shells have been observed in limestone, is in a black and very
hard description, at the Western foot of the Gede, near the kampong Kembang
Kuning, in which the forms of Pectens and other bivalve shells may be seen at
an elevation of about 1,000 feet above the Sea.
The range of the Gunung Seribu
runs out N.N.E. from the eastern base of the Gede and extend in that direction
for 10 or 12 miles, thus forming a snug and quite bay of the parts now called
Jasinga, which during the intermission of volcanic activity would be highly
congenial to the habits of Testaceae, whose numerous remains still exist, and
to those zoophytes, by which lime is supposed to be elaborated. The
supposition, that Jasinga has formed a bay of the Sea at no very distant
geological period is further borne out by the little elevation, which it yet
possesses above the Sea, although at the foot of the mountains and removed
above 30 miles from the North shore, towards which the slove is very gradual.
It is similarly situated, with respect to the Western ocean, about Welcome and
Papper bays, at which point the Sea is supposed to have formerly enterd and,
running between the Southern hills and the mountains as islands accross the
bay, to break the force of the N. W. Mousoon.
According to the Mr. Horner’s
observations, the Demang’s house at Jasinga is only 352 feet above the Sea ; at
Sajira, on the Chiberang, only 11 miles West, this height has decreased to 187
feet and at Lebak, 16 miles further in the same direction, the elevation of the
residents-house is only 76 feet ; the waters from this place still find their
way to the North shore. Westward still from Lebak, the whole district of
Panimbang is reported to be so low, that in the wet mouseen the Chiliman
readily overflows its banks and a great part of the country becomes little
better than a swamp, the couse of so much fever and mortality to the native
inhabitants. The Chiliman flows into the Western ocean.
Volcanos have a tendency to
destroy themselves and, after remaining for centuries in a state of great
activity, to lose of outward appearance of energy, their vents becoming closely
shut up by the accumulation of their own debris. The volcanic forces however go
on increasing with-in and, finding no longer their accostomed egress, open for
themselves fresh vents at more distant points, or else swell and gain
additional space by upheaving en masse the solid strata, by which they are shut
in ; an operation of this kind may have coused the rise of the Westen end of
Java, therby excluding the sea from its ancient do-minions. That the igneous
agents are not yet extinct under Jasinga, may be inferred from the hot springs,
that are occasionally met with.
On the Westen slope of the Gede
two separate apertures discharge waters of the temperature of 97°
fahrenheit, one of which has a very strong smell of Sulphur and about five
miles West of this near the Kampong Sea in Bantam, is a well, whose waters
indicate a temperature of 134°. The water of this latter well, when
drawn out and left to cool, affords no other taste than that of ordinary water
after boiling and only a very slight smell of sulphur is experienced. The
waterbubbles up through a ledge of rocks, to which it imparts a white color,
which however shows no disporition to effervesce with acids. When silence is
observed and attention paid, a low, dull, rumbling sound is head at intervals
and this is immediately followed by an emission of air bubbles and quite again
successds. Though the taste of the waters is insipid to man, the Buffaloes and
other animals are fond of sipping it, when it has cooled. All over the country
there are a number of springs, known by the same of seuseupan, at which, in
preference to the river, all animals drink; these springs are now cold and have
no extraordinary smell or taste, yet must possess some peculiarqualities, as
the buffaloes are known to thrive better from frequenting them. The water of
all these springs may have one common origin ; but from the nature of the rocks
and strata they pass through, some part with their beat more readily than
otehrs; while again those, which make their way accross the more decided
submarine formations, arrive at the surface at the ordinary temperature of the
atmosphere.
Large quantities of silicified
wood are every where met with, known by the name of Batu Sumpur, as the natives
suppose, that this hard wood alone is fossilized ; but the variety of grain,
which is still preserved entire, does not countenance the belief, that the
Sumpurs (COLBERTIA and CAPELLIA) are the only trees, on which this process has
acted.
There are positions; which seem
more favorable for silicification than others. A good drainage of percolating
waters appears necessary, so that when that medium has deposited the silex,
which it holds in solution, it may readily run off and make way for a fresh
supply. Consequently the greatest quantities are found lying above the more
compact tuff and covered by enveloved in the loose, porons, superficial earth
or volcanic sands, and many of these emit fire when struck by iron. On the
contrary such wood, as has been entangled in the more compact and solid stuffs,
still remains soft and may be readily cut away with a knife and, when fresh,
presents every appearance of common charcoal saturated with water and easily
crumbles in the hand ; these however, when preserved dry for a few months,
attain considerable hardness and then offer effectual resistance to the knife,
which extracted them from their original position ; cases have been observed of
the two varieties being almost in contact, when the one imbedded in the close
tuff was soft and friable, whereas its neighbour, that merely reposed on that
formation, had become perfectly hard and solid.
All these woods may have been
originally carbonized by volcanic action and thus preserved from putrefaction ;
this supposition will account for the logs of stone of 10 to 12 feet in length
being found cracked across the grain, in irregular lengths, yet still lying in
the same continuous straight line. A mass of charcoal would easily give way
under an increase of pressure ; but that the hard silex stone, often of 1½
or 2 feet diameter, should so break, can hardly be conceived. That pressure has
been experinced, when in a soft state., is shown by the flattened appearance of
some speciments. The black color has drained off with the water percolating
through them : many lumps, which have become externally white or of a reddish
hue, are still black at the centre.
Jasinga,
27th November 1837
JONATHAN
RIGG
Source : Verhandelingen Van Het Bataviasche
