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sometimes empty, but in the lower portions of the rock usually filled,
or partly filled, with the earths and clays above mentioned, or a
siliceous and argillaceous dust, often stained by oxide of iron. A
species of black bole, carbonized wood and carbonate of lime some-
times occur, but rarely, in these cavities. Minute drusy crystals of
quartz not uncommonly line the interior. The walls separating the
cavities are composed of an argillo-siliceous paste, often strongly
impregnated with iron and frequently imbedding gritty particles of
quartz. The oxide of iron prevails sometimes to such an extent as to
approximate a true ore of iron, and the nodules are often separated
and smelted by the natives in preference to using the magnetic iron
ore, which is more difficult to reduce, from its greater purity, ^^'hen
the whole mass is charged with iron and very vesicular (not unfre-
quently the case) it might easily be mistaken for iron slag. The
colour of the parietcs separating the tubes and cells, which in the less
ferruginous varieties is a light brick-red or purple, changes into a liver-



26 GEOLOG V

brown, having externally a vitrified or glazed aspect ; while the surface
of the interior cavities puts on iridescent hues. The walls of these
cells are sometimes distinctly laminated.

The air-exposed surfaces of laterite are usually hard and have a
glazed aspect, and the cavities are more empty than those in the lower
portion. A few inches or more below the surface the rock becomes
softer, and eventually as it descends so sectile as to be easily cut by
the native spades, but hardens after exposure to the atmosphere.
Hence it is u.sed largely as a building stone in the districts where it
prevails, and to repair roads. P>om its little liability to splinter and
weather (time appears to harden it), it is a good material in fortifica-
tions. The accumulation of the clays and lithomargic earths in the
lower portions of the rock, which absorb some of the moisture per-
colating from above, renders the mass soft and sectile. These earths
doubtless existed once in the upper cavities of the rock, from which
they have been gradually removed to. the lower strata by the downward
action of the water of the monsoon rains. They accumulate at various
depths from the surface and form impervious beds, on the depressions
of which the water collects, forming the reservoirs of the springs we
often see oozing from the bases and sides of lateritic hills and cliffs.
Some of the tubes and cavities are cu/s de sac, and do not part with
their contents ; but the generality have communication with those
below them, either directly or indirectly.

Associated Minerals. — Nodular, reniform and pisiform clay iron ore
occur pretty generally distributed. Large beds and nests of litho-
margic earths, and white porcelain earths, are not uncommon.

Older AlluYium. — The designation of alluvium is here used in its
extended sense to indicate certain beds of gravel and sand that are
occasionally found covered by the regur deposit, and which occur in
such situations as not to be accountable for by the agency of existing
transporting powers ; simply prefixing the term " older " to distinguish
it from the alluvium now .forming from the disintegration of rocks
washed down by the rains and springs, and transported by rivers and
local inundations.

In the valleys of the Bhima, Krishna, Tungabhadra, and other
large rivers are occasionally seen beds of alluvial gravel elevated beyond
the highest existing inundation lines. Some of these deposits may be
ascribable to shifts from time to time in the course of the river's bed ; a
few to the action of rain in bringing down alluvium from the mountain
sides ; but the majority appear to have been accumulated under con-
ditions not now in existence ; probably, during the slow upheaval of
the AVestern Ghats and plateau of the Dekhan, when the water



OLDER ALLUVIUM 27

occupied a much greater extent than at present. In many places the
rivers have cut their way through these deposits ; in others, channels
exist of rivers, where now no water flows, or but a diminutive stream-
let. Thus the Moyar valley, which runs along the table-land of Mysore
by the base of the Nilgiris, differs entirely from a common mountain
glen. Though a mile or more in breadth at some points, yet it is rather
a ravine or fosse cut in the plain and not hemmed in by mountains. It
opens out into the lower plain of the Carnatic at the Gajalhatti pass :
the sides are precipitous, and its bed very much like the deserted
channel of a river. The only stream now flowing in it is the Moyar,
which, even in the monsoon, does not fill one hundredth part of its
breadth and height : yet this singular excavation, extending some
thirty miles in length, is unquestionably a waterworn channel. It is
no fissure ; for its bed is quite solid and connected and composed of
strata of the hypogene rocks.

Hegnr or Black Cotton Clay. — This singular deposit, which in sheets
of considerable thickness covers at least one-third of Southern India, is
less common in Mysore. The plains occupied by the cotton soil are in
general marked by their horizontal sea-like surface and almost treeless
aspect. It covers the kunker and gravel beds just described, and is
generally seen as a surface soil ; but if we examine the edges of great
sheets they will generally be found to dip for some distance under the
recent alluvium, which conceals and replaces them as a surface soil.
It not only covers extensive plains, but the tubular summits of hills
overlooking those of the sandstone and limestone, newer trap and
laterite formations, far above the present drainage level of the country :
it covers all rocks from the granite to the laterite and kunker, and often
fills up depressions and chinks in their surface.

The purest regur is usually of a deep bluish-black colour, or greenish
or dark greyish black. The quantity of iron it contains is not sufficient
to account for the black colour of this soil, which may be partly attri-
buted to the extractive or vegetable matter it contains. The regur is
remarkably retentive of moisture ; a property to which is ascribable
much of its fertility. During the dry season, when the crops are off the
ground, the surface of regur, instead of presenting a sea of waving
verdure, exhibits the black drear aspect that the valley of the Nile
puts on under similar circumstances, and whicli powerfully reminds
one of the regur tracts of India. Contracting by the powerful heat
of the sun, it is divided, like the surface of dried starch, by countless
and deep fissures, into figures usually affecting the pentagon, hexagon
and rhomboid. While the surface for a few inches in depth is dried to
an impalpable powder raised in clouds by the wind and darkening the



28 GEOLOG y

air, the lower portions of the deposit, at the depth of eight or ten feet,
still retain their character of a hard black clay, approaching a rock,
usually moist' and cold ; when the surface dust has a temperature of
130°. In wet weather the surface is converted into a deep tenacious
mud.

The purest beds of regur contain few rolled pebljles of any kind ;
the nodules of kunker we see imbedded have probably been formed by
concretion from the infiltration of water charged with lime ; and it is
only near the surface that the regur becomes intermingled with the
recent alluvium of the surrounding country, or in its lower portions,
where it becomes intermingled with the debris of whatever rock it
happens to rest on, — trap and calcedonies in trappean districts ;
granite, sandstone, pisiform iron ore and limestone, in the plutonic
and diamond sandstone areas. It sometimes exhibits marks of
stratification.

That the regur of India is an aqueous deposit from waters that
covered its surface to a vast extent, there is little doubt : but it would
be difficult to point out at the present day the sources whence it
derived the vegetable matter to which in great measure it owes its
carbonaceous colour, and the rocks from the ruins of which its remain-
ing components were washed.

Kunker. — The calcareous deposit termed kunker^ is irregularly dis-
tributed in overlying patches. No tract is entirely free from it, with
the exception, it is said, of the summits of the Nilgiris. It occurs,
however, at the height of 4,000 feet above the sea among the ranges on
the elevated table-lands. It is most abundant in districts penetrated
and shattered by basaltic dykes, and where metallic development is
greatest. It is perhaps least seen in localities where laterite caps hypo-
gene or plutonic rocks. It occurs filling, or partially filling, fissures and
chinks in the subjacent rocks, in nodular masses and friable concretions
in the clays and gravels above the rocks, and in irregular overlying beds,
varying from a few inches to forty feet in thickness. It has been found
at the depth of 102 feet below the surface of the surrounding country,
prevails alike in granite, the hypogene schists, the diamond sandstone
and limestone, and in the laterite : hence the springs which deposit it
must bring up their supply of calcareous matter from sources deeper
beneath the earth's crust than the limestone.

The older kunker is usually of a light brownish, dirty cream, reddish
or cineritious grey tint ; sometimes compact and massive in structure,

* A Hindustani word .CJo but of Sanskrit extraction, signifying a nodule of lime-
stone or pebble of any other rock.



MODERN ALLUVIA 29

but more usually either of a nodular, tufaceous, pisiform, botryoidal, or
cauliflower-like form. Its interior is sometimes cancellar, or slightly
vesicular ; but compact or concentric in the pisiform and nodular
varieties. Its interior structure is rarely radiated. When compact it
resembles the older travertines of Rome and Auvergne. It aggregates
in horizontal overlying masses, usually intermingled with the soil
without much appearance of stratification. It is broken up and
used as a rough building stone in the bunds of tanks, walls of
inclosures, &C., by the natives, and is universally employed to burn into
lime.

In the banks of rivers it is often seen concreting in stalactiform
masses round the stems and roots of grasses, which, decaying, leave
casts ot carbonate of lime. This lime, held in solution and suspension
by existing streams, mingling with the fine particles of sand and ferru-
ginous matter in suspension, sets under water like pozzolana ; and unit-
ing the shells, gravel, sand, and pebbles in the bed and on the banks,
forms a hard and compact conglomerate.

Its origin may be referred to the action of springs, often thermal,
charged with carbonic acid, bringing up lime in solution and depositing
it as the temperature of the water gradually lowered in rising up to the
earth's surface or in parting with their carbonic acid.

Modern Alluvia. — Where regur does not prevail, the ordinary soils
are distinguished by a reddish tinge, owing to the great prevalence of
oxide of iron in the rocks of which they are, in great measure, the
detritus. Patches of white soil occur, and are usually the consequence
of the weathering of beds of quartz, or composed of kunker, which
abounds so generally, and enters into the composition of almost every
variety of soil. These white soils are characterized by sterility. In
tracts of country shaded by eternal forests, for instance the Ghats, and
sub-ghat belts, a dark vegetable mould prevails, — the result of the suc-
cessive decay and reproduction of vegetation for a series of ages, under
the stimulating alternations of excessive heat and moisture. In such
regions, where unsheltered by forest and in exposed situations, the
soil is either lateritic or stony according to the nature of the subjacent
rock.

At the bases of mountain ridges we usually find an accumulation of
large angular blocks, composed of the same rocks as the hills down
whose declivities they have rolled in weathering. At a greater distance
from the base in the plain, these are succeeded by pebbles, whose
reduced size, mineral composition, and worn angles proclaim them to
have travelled from the same source, diminishing in bulk the further we
recede from the mountains, until they pass, by the gradations of grit



30 GEOLOGY

and sand, into deposits of a rich clay or loam. Such are the gradations
generally to be traced in the modern rock alluvia, and which strikingly
distinguish them from the vegetable soil of the forest tracts and the
regur, which are often seen in the state of the greatest richness and
fineness of composition at the very bases of the hills and resting
immediately on the solid rock.

The alluvia brought down by the streams from the Western Ghats
flowing easterly to the Kay of Bengal, are usually composed of silt,
sand and gravel — detritus of the rocks over which they have passed :
they almost always contain a considerable portion of lime derived from
the springs which supply them, and from the limestone and kunker
beds over which most of them flow. The alluvia of the rivers of
the western coast are of a more carbonaceous and less calcareous
character, owing to the greater absence of lime in the formation, and
the dense forests and luxuriant vegetation which almost choke their
passage.

During the hot season, when the surface of the alluvial sand in the
beds of the rivers and rivulets is perfectly dry, a stream of clear water
is frequently found at various depths below them, stealing along or
lodging in the depressions of some impervious layer of clay or rock, to
which it has sunk through the superincumbent sand. So well is this
fact understood by natives, that in arid, sandy tracts, where not a drop
of water is to be seen, they will often be enabled to water whole troops
of horse and cattle by sinking wells a few feet deep through the sands
of apparently dried-up rivulets.

The benefit resulting from the admixture of lime into soils consisting
almost solely of vegetable, siliceous, or argillaceous matter, is too well
known to be dwelt on here ; and it is a remarkable and bountiful pro-
vision of nature in a country like Southern India, where limestone is so
rarely seen in the rocks from which a great part of its soil is derived,
that innumerable calcareous springs should be constantly rising through
the bowels of the earth to impregnate its surface Avith this fertilizing
ingredient.

The alluvia of Southern India are remarkable for their saline nature.
The salts by which they are impregnated are chiefly the carbonate and
muriate of soda, which prevail so much (particularly in mining districts)
as to cause almost perfect sterility. The carbonate appears on the sur-
face covering extensive patches, in frost-like efflorescences, or in moist
dark-coloured stains, arising from its deliquescence in damp weather or
by the morning dews. Where such saline soils are most prevalent there
will be usually a substratum of kunker, or nodules of this substance,
mixed with the soil ; and there can be little doubt that their origin may



MODERN ALLUVIA 31

be referred to the numerous springs rising through the fissures or laminae
of the subjacent rocks, some charged, as already noticed, with carbonate
of lime, and others with muriate of soda and sulphate of lime. The
carbonate of soda, like the natron of Egypt, is the result of a mutual
decomposition of the muriate of soda and carbonate of lime. It may
be as well to remark that muriate of lime is invariably found in the
saline soils of India, which are known to the natives by the term chaulu.
The soda soil is used by the dhobis, or washermen, to wash clothes with,
and hence is called washermen's earth ; it is also employed by the
natives in the manufacture of glass.

Both the carbonate and muriate of soda are found mingled in varying
proportions, in white efflorescences, in the beds and on the banks of
springs and rivulets.

Nitrous Soils. — Soils impregnated with nitre are found on and around
the sites of old towns, villages, &c. Here a vast quantity of animal
matter must gradually have been blended with the calcareous and vege-
table soil : from their decomposition the elements of new combinations,
by the agency of new affinities, are generated : — nitrogen from the
animal, and oxygen, &c., from the vegetable matter. The nitric acid
thus produced combines with the vegetable alkali, forming the nitrate of
potass, while its excess, if any, combines with the lime, forming a deli-
quescent salt, — the nitrate of lime. The affinity lime has to nitrogen
and o.xygen materially assists the formation of the acid by their com-
bination. The natives of India, in their rude manufactories of salt-
petre, act upon these principles without being aware of their rationale.
Having collected the earth from old ruins, or from places where animals
have been long in the habit of standing, they throw it into a heap
mingled with wood ashes, old mortar, chunam, and other village refuse ;
and allow it to remain exposed to the sun's rays and to the night dews
for one or two years, when it is lixiviated. The salt obtained is not very
pure, containing either the muriate and sulphate of soda or potash, or
nitrate and muriate of lime.

Nitrous soils are easily recognized by the dark moist-looking patches
which spread themselves irregularly on the surface of the ground, and
by capillary attraction ascend walls of considerable height. They are
more observable in the morning before the sun has had power to dissi-
pate the dews.

Auriferous Alluvia. — The alluvium brought down by the rivers
flowing easterly towards the Bay of Bengal is usually silt, sand, or
calcareous matter, — detritus, as before observed, of the rocks over which
they pass ; while that of the rivers flowing westerly is of a more carbon-
aceous character. Most of these alluvia are auriferous, particularly those



32 GEOLOGY

of the Malabar and Canara coasts, but grains of gold are also found in
considerable abundance in the alluvial soils of Mysore.

Betmangala lies on the eastern flank of the principal gold tract,
which, according to Lieutenant Warren, who examined this district in
1802, extends in a north-by-east direction from the vicinity of Budikote
to near Ramasamudra. The gold is distributed in the form of small
fragments and dust throughout the alluvium covering this tract.

At Markuppam, a village about 12 miles south-west from Betman-
gala, were some old gold mines, worked by Tipu without success. The
two excavations at this place demonstrated the great thickness, in some
parts, of these auriferous alluvia. They were 30 to 45 feet deep
respectively. There can be little doubt that the auriferous black and
white stones in these mines were fragments from the gneiss, granite and
hornblende schist which base this auriferous tract, and constitute the
singular ridge which runs through it in a north and south direction,
and which may be regarded as having furnished most of the material.^
of the reddish alluvium on its east and west flanks, and therefore as the
true matrix of the gold. The orange-coloured stones were caused by the
oxidation of the iron in the mica.

This auriferous range on the table-land of Mysore may be traced to
the Eastern Ghats, southerly, by the hill fort of Tavuneri, to the south
of Kaveripatnam matha in the Amboor valle}'. Two passes, however,
break its continuity near Tavuneri. To the north it appears to
terminate at Dasarhosahalli ; though the line of elevation, taking a
gentle easterly curve, may be traced by the outliers of the Betarayan
hills, Amani konda or Avani, Mulbagal, Kurudu male, Rajigundi to
Ramasamudra in the Cuddapah collectorate, a little west of Punganur.

Dimes. — Sand dunes are not confined to the coasts, but are seen on
the banks of the larger rivers in the interior, as at Talkad on the
Kave'ri. During the dry season, the beds of these rivers, deriving but
a scanty supply of water from perennial springs, usually present large
arid wastes of sand. These are acted upon by the prevailing westerly
winds, which blow strongest during the months of June, July, and
August, and raise the sand into drifts, which usually advance upon the
cultivation in an easterly direction. The advance of these moving
hills is usually very regular where no obstruction presents itself, such as
high bushes, trees, hedges,



Online LibraryB. Lewis (Benjamin Lewis) RiceMysore: a gazetteer compiled for government (Volume 1) → online text (page 5 of 98)