페이지 이미지
PDF

Angular fragments of granite, gneiss, and hornblende schist sparingly scattered among the pebbles of the lime-stone formation on the river bank, attest the proximity of these rocks. Rectangular blocks of a greenish crystalline limestone with reddish argillaceous, and arenaceous veins;–imbedding iron pyrites in cubic crystals. It is at first sight difficult to pronounce whether this rock is hornblende schist, rendered calcareous by contact with the lime-stone, or lime-stone which has taken up hornblende. I have little doubt that these blocks are from the junction line of these two rocks. It effervesces but feebly with acids. The sistmah at Paugfoor—The Moorish fort and pettah of Pangtoor stand on the right bank of the Kistnah in the Nizam's territories, the S. frontier of which has been just crossed about half a mile N of Kurnool. The bank here is formed by two perpendicular cliffs of light bluish grey lime-stone, in nearly horizontal strata, divided by vertical fissures from summit to base, like those in the sand-stone ranges of Gundicota and Cuddapah. The Kistnah here does not appear broader than the Tumbuddra at Kurnool, which, at the narrowest part between Raza and the fort, measures exactly 616 yards from bank to bank. The river was filled with the muddy freshes of the monsoon, and running, near Pangtoor at the rate of about 24 inches per second. A velocity calculated strong enough to transport pebbles the size of an inch in diameter; velocity, No. 6, of the scale laid down by the talented Secretary of the Royal Geographical Society,+Col. Jackson. It is, however, clear from an inspection of the size of some of the pebbles in the river's bed, (some of which are as large as a hen's egg,) that the velocity must often be increased to No. 7 of the scale; or to 36 inches per second. The temperature of the water is the same as that of the Tumbuddra (a foot below surface), viz., 79° Faht. exceeding by one degree the average temperature of rain-water in this part of the country. The temperature in the shade at the time of observation 86°; time, 2 p. M. A tumblerful of the muddy water deposited, after standing 6 hours, orth of its bulk. The sediment was a fine reddish silt, which effervesced with acid ; but is less calcareous than that of the Tumbuddra. The reddish colour of the deposit brought down by the Kistnah, a river which completely traverses the great overlying trap region, is worthy

[ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors]

of notice by those geologists who consider the regur or black soil of
India as a fluviatile deposit; or as the washings of trap rocks.
The still unflooded parts of the river bed consisted of collections of
light-coloured sand and silt, and accumulations of pebbles from the size
of a No. 4 pellet to that of an egg, as before stated. These pebbles
were chiefly of quartz, calcedony, cornelian, agate, and Mocha stones:
fragments of onyx and sardonyx rare and small. Also common and
semi-opal ; heliotrope, and jaspers of various shades of red, brown,
green and yellow.
I picked up some rolled bits of radiated zeolite, limestone, pegmati-
tic granite with reddish felspar, and find nodules of cream-coloured
and greyish white kunker.
Nothing but the very toughest fragment of the overlying trap,
whence these calcedonies and zeolites have been washed for a distance of
not less than 100 miles to the N. W. have remained entire; these
debris we must look for nearer to their situs, or try to recognize it in
the sands: thus following the maxim in geological dynamics; viz., that
in alluvial beds the most indurated portions of transported matter
will always be found at the greatest distance from their situs.
I am informed that in the bed of the river nearer its embouchure,
the cat's eye and diamond are found in the Polnad Circar, and I know
that the last named gem is found in the bed of the Kistnah in the
eastern parts of Kurnool near Siddeswar, and still further east beyond
the wilds of Perwut and the diamond mines of Purtial, Moogaloor,
Codavacutloo, and Oostapully, which are on the N. bank of the Kistnah ;
the diamond I have no doubt, has been washed out of the diamond
sandstone formation of these tracts east of Paugtoor and Kurnool; but
the cat's eye, like those in Ceylon, is probably from the gneiss or grani-
tic rocks. -
From the Kistnah to Judeherla, 60 miles northerly.—The lime-
stone formation extends about three miles in the plain north of the
Kistnah, when granitic rocks are met with associated with gneiss in
the vicinity of Myapore. This granite rock spring up irregularly
from the surface of the plain, leaving often level spaces between each
hill, but those of gneiss usually form short, and more regularly conti-
nued ridges.
These elevations, however irregular in detail, have a general direction

of E. S. E., which has apparently determined that of the Kistnah across the peninsula after escaping from the overlying trap formation. One of the peaks rises from the rest like truncated come. As I was obliged to pass the granite and lime-stone junction line by night, I am unable to afford a description of the disturbance, or of the mineral alteration in the latter rock which might be anticipated. A succession of these rocks continues to be crossed until Judcherla is approached, 60 miles north from the Kistnah, when they sink into smooth undulating plains with an occasional granite rock starting up. The rocks in the centre of this granitic zone, in the vicinity of Paungal, attain the highest elevation, (viz. about 1000 feet above the plain.) The highest which I had an opportunity of measuring trigonometrically, did not exceed 950 feet. The granite is generally small-grained, with reddish felspar, often coloured (as near Paungal) with actinolite or chlorite in quartz and felspar veins. Here also a graphic granite occurs in the gneiss. Granitoidal gneiss (for the transition from granite to gneiss is imperceptible, and the alteration by contact under great heat mutual) is seen in low and rather smoothly swelling hills, around the bases of the loftier granite peaks. The basaltic green-stone dykes have usually an easterly direction :and, as a general rule, large dykes are crystalline towards the centre, and compact at the edges like the lava dykes of Somma and Etna. I observed crystallized epidote on a dyke at Paungal. Another dyke is seen close to the west side of the town of Judcherla, about 40 paces broad, and may be traced westerly as far as the eye can reach. From Judcherla to IIydrabad, 59% miles northerly.—From Judcherla the country is open; the formation gneiss, penetrated by granite and basaltic green-stone. At Nagumpilly the fort stands on a bed of quartz in the granite which is intersected by a basaltic dyke containing hypersthene. A second dyke is seen between Nagumpilly and Furrucknugger; and two others a little north of Furrucknugger. This latter is from 30 to 50 paces broad, and takes a zigzag direction towards the east. Abundant efflorescences of matron take place on the surface of the soil in the vicinity. Beds of quartz become more frequent in the granite as Hydrabad is neared. At Nagumpilly, just mentioned, 17 miles south of Hydrabad, the bed or vein runs east by south, and in many places is amethystime. In a vein of quartz near Palmacul the purple colour of the amethyst is more decided ; and, at this place, I detected, in combination with oxydulated iron ore, oxide of manganese, which I have little doubt im, parts this beautiful tinge to the quartz. At Shemsabad, about 19 miles south from Hydrabad, another vein of similar quarz occurs. Hydrabad.—Hydrabad is situated in the lowest part of a shallow flat valley, bounded by irregular granite rocks which rarely rise more than 400 feet above its general level. According to the barometric measurements of the Trigonometric survey, Hydrabad is 1672 ft. above the level of the sea; Secunderabad 1837 ft. ; and the granite rock of Moel Ally 2017 ft. The Mussy river flows easterly through this valley; and, by a transverse break through the north and south ridge of Bhonageer, about 18 miles to the eastward, to the Kistnah which it joins at Wujerabad, about 17 miles west of Amrawutty. The plains around IIydrabad are often crowded with tors, logging stones, and globular masses of granite, which Broignart, on the auth rity of De Luc, has pronounced to be boulders; but which are, without doubt in situ, as I have stated in a former paper on supposed boulder formations in South India. The prevailing colour of the granite is reddish, owing to that of the felspar, which predominates almost to the exclusion of quartz.-The latter mineral is not wanting in the granite ; but, from some unknown cause in nature's laboratory, has been segregated in large veins and beds, instead of being diffused in grains throughout the substance of the rock. These veins, or beds, are still more amethystine than those of Shemsabad, Palmacul, and Nagumpully. Mr. Malcolmson is of opinion that the crystallized specimens found near the European barracks are fit for the purposes of jewellery. Another amethystine vein occurs, according to Christie, near the British native cavalry lines. Mr. Malcolmson has found it at Bekonurpett, about 60 miles north of Hydrabad, and I have traced it 46 miles westerly to Sedashipett;-and 47 miles southerly to the vicinity of Nagumpully. It occurs often at Hydrabad in hexagonal pyramidal prisms filling cavities in quartz. Voysey mentions their occurrence at Pitlam and Ghazipettah.

Four or five dykes of basaltic green-stone, or possibly the ramifications of one enormous coulée, traverse the granite rocks of Hydrabad with a general easterly direction. One of them runs through the tombs of the kings at Golconda, and is probably identical with that seen six miles to the eastward between the British Residency and the great tank of Hussain Saugor. From the blasted and chiselled appearance of some of the blocks and mineral resemblance, this dyke has evidently contributed part of the material for the dark and highly polished slabs of which the royal tombs are constructed. It must not be confounded, as has been done by Malcolmson,” with the dark talcose rock of the pillars supporting the tombs of Hyder and Tippoo at Seringapatam. The rock on which stands the celebrated fortress of Golconda is of a granite resembling that of Gooty, with reddish felspar, quartz in small grains, dark dull green scales of mica, and a little hornblende. Actymolite, both crystallized and blended with compact felspar and quartz, occurs in veins pretty generally throughout the granitic rocks of Hydrabad.—A rough trigouometric observation from a paced base makes the rock of Golconda 450 ft. above the general level of the plain. Soil.—The surface soil, in the vicinity of Hydrabad, is the reddish granite alluvium, partly washed down from the sides of the neighbouring hills, and partly the debris of the decaying rocks on the spot. It is originally reddish in colour, but often altered by cultivation and manuring into an ashy grey. It generally contains a small proportion of calcarious and saline matter, derived, probably, from the infiltration of water which has held these minerals in solution. The alluvium brought down by the Mussy (here from 100 to 180 yards broad), from the westward, is a reddish sand and silt; also beds of pebbles chiefly granite, nodules of ferruginous clay, (apparently from lateritic beds,) and kunker. Voysey states that this river rises in a gramitic country, (according to Hamilton, it rises about 43 miles W. from Hydrabad, at the Anantghur pagoda,) and attributes to this cause the circumstance of its not having black alluvium or regur on its banks. (Wide my remarks on the Kistnah in this paper). It may be here stated that the Tumbuddra

* Madras Journal, July, 1836, p. 199.

« 이전계속 »