« PreviousContinue »
soothing agent, and it is known to be eaten in India in the form of “edible clay”. Chlorite, being unctuous, soft and insoluble, would be neutral, and the quantity present is almost imperceptible.
The catchment area consists entirely of the Darjeeling gneiss, a banded rock consisting of quartz, felspar, biotite and muscovite mica, garnet, chlorite, tourmaline and a patite. Of these minerals only felspar and mica are decomposable by ordinary atmospheric agents, and as the water in the catchment area runs rapidly through it in torrential hill streams, hardly any salts can be dissolved, and, in point of fact, Darjeeling water is notably “soft”.
When I visited the reservoir, water was running strongly into it, after some days of heavy rain, but the water was crystal clear though carrying much leaves and other vegetable debris, and coarse sand comprising granite, quartz, felspar and mica. Much of this is retained in a small tank provided with baffle-plates, where the supply enters the reservoir, and any left will promptly settle in the reservoir close to the inlet.
To conclude, the Darjeeling water is markedly free from mineral impurities, either solid or dissolved, but carries much floating vegetable matter after rain. Water supply,
68. Mr. Crookshank was deputed to examine Belgaum cantonment, the water supply of the Belgaum cantonment Bombay.
on behalf of the Southern Command. He reports that Belgaum is situated on Deccan trap flows which form here a thin skin over Dharwar schists. Between these two main formations is a variable thickness of gravel and clay which probably represent the Lameta beds of other parts of India.
The present water supply is derived from numerous wells tapping the weathered surface of the basal trap flow. It is unlikely that further wells tapping this horizon would add much to the total water supply of the area, as the existing ones probably extract the bulk of the water that soaks into the rocks of this horizon during the rainy season each year.
Mr. Crookshank recommended an experimental boring through the lowest trap flow into the gravels which separate it from the underlying Dharwars. The depth to the base of the lowest flow in the Nagzeera area is probably less than 200 feet. Water, if any, tapped by such a boring would probably be perennial, and its extraction would be unlikely to affect existing well-water supplies.
Subsequent information is to the effect that the beds between the Deccan trap basement and the schists have not yielded water in the Nagzeera boring. In the event of the boring at Nagzeera proving a failure, Mr. Crookshank considered that a larger scheme for supplying water both to the civil and the military should be investigated.
Two perennial streams exist within six miles of Belgaum—the Mogitra nala and the Markandeya river. The former flows over a gravel bed, but well-sections show that Dharwar schists underlie the gravel at no great depth. It is suggested that a trench be made across the nala bed down to the schist at some time during the hot weather, and that tests be made to see how much water passes.
If the supply is adequate it would be a simple matter to bring it in to Belgaum.
Failing an adequate supply a storage reservoir would have to be constructed. This might be done at some suitable place further down the Markandeya river or in the valley of the Markandeya below the Poona-Belgaum road. In the first area the reservoir could easily be founded on the impermeable Dharwar schists and in the second on the equally sound Purana quartzites. The selection of the dam site would be mainly a matter of engineering convenience.
69. At the request of the military authorities Mr. H. Crookshank was sent to Jubbulpore to investigate the possibilities of finding
Water-supply, Jubbul- water in the vicinity of Kerendi bill east of pore, Central Provinces. that city.
He reports that the geology of the Kerendi area is almost identical with that near Bara Simla where 10 very successful borings have already been sunk. He considers it certain that valuable supplies of water can be made available by drilling on the sites selected by the military near Kerendi hill. He is unable to say whether the results will be as good as those already obtained in the Bara Simla area, but he considers that they should be quite comparable. Some improvement in the yield of bore holes should be obtainable by sinking them to a greater depth than has been done so far, but whether the extra yield would justify the expense he is unable to say. The maximum possible yield would only be reached on boring through the Gondwana rocks exposed at the surface to the underlying granitic The depth down to the granitic rocks is not known,
It is unlikely that the withdrawal of the amount of water required by the military will seriously reduce the underground water level in the Jubbulpore area.
70. At the instance of the Director of Agriculture, Punjab, Mr. H. M. Lahiri was asked to visit the area around Khair, (31° 12' : 75° 55') Water-supply, Nurpur
in the Nurpur tahsil of the Kangra district tahsil, Kangra district, and to report on the geology and water supply
possibilities thereof. Mr. Lahiri reports that the site selected by the Agricultural Department for sinking a trial bore-hole for water lies on clays, loams and gravels of probable sub-Recent age, which occupy a large area in the valley of the Buhl Khad and its tributaries in the eastern part of sheet 43P/16. The depth of these beds at the proposed site is unknown and can be ascertained only by actual boring.
Examination of the existing wells of the area has shown that while the sub-surface water table only about one mile to the north or south-east of the proposed site is, in the winter months, quite close to the ground level, that at Khair itself is at least 50 feet below the stream bed east of the village. The depth of the valley deposits at the site is not known, but whatever it may be, from various considerations, the chief amonget which is the proximity of the place to the main water-parting and the consequent smallness of the collecting surface, the chances of obtaining a satisfactory supply of water from these beds are rather remote.
Mr. Lahiri has also considered the possibility or otherwise of obtaining artesian or sub-artesian water in the area. clinal structure of the Siwalik beds below the Buhl valley deposits, the the porous character of the
outcropping Siwalik rocks, their alternation with clay beds and the general lower level of Khair than that of the rock outcrops on either side, are apt to raise expectations of obtaining such water.
But when the Siwalik beds cropping out to the south-west of Khair are followed down along their dip towards the north-east, they will probably be found at a minimum depth of 500 feet under Khair and accordingly it would be necessary to sink a bore-hole deeper than this in order to tap water from them. Also, frequently occurring boulder-beds are likely to give trouble in boring. Further, it is not known whether the Siwalik beds
as porous below the valley deposits they
Nor is it known with certainty if the clay beds seen in the outcrops continue north-eastwards under Khair. In these circumstances, Mr. Lahiri does not think it advisable to undertake any deep boring here on the chance of obtaining artesian or sub-artesian water.
Mr. Lahiri notes that while the prospects of obtaining sufficient water at Khair are poor, only about 11 mile to its south-east, at the junction of the Dhial ka nala and the Rahen nadi, shallow hand-dug wells are known to yield an inexhaustible supply throughout the year.
The yield of a well situated at the junction may be increased, if desired, by running infiltration galleries up the Rahen nadi. This site commands a large collecting surface and the annual rainfall being fairly high (62 inches), the supply is expected to be satisfactory.
71. In advising the authorities of the Jashpur State regarding the question of a well for the proposed water-works at Jashpurnagar
(22° 53' : 84° 8') Dr. Dey observes that the Water-supply, Jash- rocks around Jashpurnagar are mainly granitic pur State, Eastern States Agency,
gneisses and laterite. The
a Mall, which nagar, is the most important factor in controlling the level of the ground-water. The present source of water-supply is derived from a number of wells dug in the permeable soil, subsoil and superficial laterite. Many of the wells become nearly dry towards the middle of the dry season.
It is believed that these wells do not reach the zone of permanent saturation but derive their supply from a temporary saturation of the upper parts of the sub-soil in the rainy season. For permanent water-supply the wells should be sunk deep enough to reach the solid bed-rock.
It has been proposed to sink a well in the doin near the Power House with the hope of obtaining a supply of 35,000 gallons per day. A study of the wells shows that the under-ground watertable at Jashpurnagar is about 30-45 ft. below the surface. these depths the wells appear to have low recuperative powers. If, therefore, the site for the new well be selected in the doin near the Power House, a large well sunk to a much greater depth than has hitherto been done at Jashpurnagar will be essential. If the supply is inadequate from the well, even after taking it down to the bed-rock, infiltration galleries may be driven in suitable directions, in order to increase the seepage surfaces.
The best source of supply, according to Dr. Dey, would be from a large well sunk in the bank of the tributary nala of the Banki nadi, south of Bartoli. The well would be on the low ground about 20 feet from the bank of the nala, above the floodwater level. The pump house would be situated on the bank of the nala and the reservoir tank may be constructed on the high ground of laterite further north. The well should be sunk deep enough to reach the bed-rock.
A second suitable site for a large well is the water-course E. N. E. of the bund near the Club House at Jashpurnagar.
This water-course has perennially running water. An adequate and reliable source of water, sufficient for the present requirements of the town, would be obtained by sinking a large well down to bed-rock, on the low ground, north of the wooden bridge near the bund.
72. Mr. Auden states that glass-sand rock occurs extensively in the older Dun gravels in the neighbourhood of Dehra. At Lach
mansidh (30° 15' : 78° 5') boulders of quartDehra Dun district, zite are broken up by hammering and sieved U. P.
through a 1/20th inch mesh. These quartzite boulders rest in a sandy clay matrix and are
probably derived from the Nagthat (Jaunsar) series cropping out north of the Dun. Their silica cement has been removed, presumably by the leaching effect of humic acids permeating the gravels, which are covered with sal forest. Similar desilicified boulders occurs on the hill west of Rajpur (seven miles north of Dehra), on Angaila hill (30° 23' : 78° 2') and on hill 2927 (30° 28' : 77° 52').
73. During the field season Dr. Dey demarcated the principal goldproducing area of Jashpur State. This area according to Dr. Dey
lies to the south of lat. 22° 39'. It is underJashpur State, East.
lain by gneissic rocks cut by innumerable veins ern States Agency.
of quartz and tourmaline-quartz rocks, and is drained by the river Ib (Eeb) and its tributaries. Sparsely disseminated gold occurs in many places but the outstanding feature of the area is the occurrence of an auriferous gravel bed under