124

WATERFALLS

[CHAP. and that of the Paikára river over the edge of the Nilgiri hills, the upper part of which is shown in the accompanying figure. In the first of these, near the town of Gairsapa, the river is precipitated over the edge of the Western Ghats to a depth of 888 feet in a single fall. Captain Newbold, who has given a graphic description of the appearance of these magnificent falls, when somewhat swollen by the rains, estimates the quantity of water then discharged over them

of Gairsapa may be justly ranked among the most magnificent cataracts of the globe. While excelled in height by the Cerasoli and Evanson cascades in the Alps and the falls of the Arve in Savoy, the Gairsapa cataract surpasses them in the volume of water precipitated; and while much inferior to Niagara in volume, it far excels those celebrated falls of the New World in height."

The falls of the Yenna in the Mahábleshwar hills are

"The height of the Cerasoli cascade is 2,400 feet; that of Evanson 1,200 feet; and the falls of the Arve 1,100 feet."

IX.]

WATERFALLS. LAKES.

125

stated by Captain Newbold to be 600 feet in height. Those of the Gokák in the South Mahratta country are 178 feet high (on the same authority); the river which, a little above the fall, measures about 250 yards across, contracts to 80 yards on the brink of the chasm, and discharges in the rainy season a volume of water estimated at 16,000 cubic feet per second.

The falls of the Káveri are of less height than the Gairsapa falls, not exceeding 300 feet; but the volume of water discharged is much greater. In Bandelkand are

several well-known falls, the largest being that of the Tonse river (200 feet in height) near Chachai. That of Bilohi about twelve miles west from the Katra pass is 398 feet high, and that of Bouti ten miles further west is 400 feet in height. At Chera Púnji in the Khási Hills, the falls of Mawsmai exceed any of the above, having (according to Dr. Oldham) a sheer fall of 1,800 feet and a broken fall of 1,000 feet more; but except after heavy rain their volume is insignificant.

Lakes are natural depressions in the surface of a country, in which the drainage water accumulates; either until, having filled the depression up to the lowest part of the encircling ridge, it reaches a channel by which the excess can flow away; or else, until it exposes so large a surface, that the natural evaporation from that surface is equal to the total quantity of water flowing into the lake in the same time. The latter case can occur only in a dry country, where the rainfall is small and the evaporation rapid in consequence of the dryness of the atmosphere. The result is, that the water of such a lake is salt; for since all the drainage water that reaches the lake carries some small quantity of salt dissolved in it, and the water eventually evaporates, leaving behind all non-volatile substances, the salt must accumulate in the lake. There are many such lakes in the great region in Central Asia to the north of the Himalaya, and even in the Tibetan Himálaya itself; as, for example, the Pangong Lake in Ladákh, near the Upper Indus valley. It appears from Major Godwin Austen's

126

SALT LAKES

[CHAP. account, that this lake was formerly one of fresh water, from which a stream flowed into the Shayok, a tributary of the Indus. Owing, however, to the increasing dryness of the country, (of which there is abundant evidence, though the cause is as yet unexplained,1) it is now isolated and much shrunken in size, and at the lower end is quite saline. The Caspian Sea and Sea of Aral are instances of salt lakes, being quite isolated from the ocean, and of such size as fairly to deserve the name of inland seas. Another and smaller example is afforded by the Dead Sea in Palestine, which occupies the bottom of a remarkable depression; such that the surface of the lake is 1,312 feet lower than that of ocean. It appears probable that at one time the valley of the Jordan, (which river flows into the Dead Sea,) was in communication with the Gulf of Akabah and the Red Sea; and that it has been isolated by the elevation of the desert of Petræa, and subsequently dried up. The waters of the Dead Sea are saturated with salt: that is, the water is incapable of holding more salt than is actually dissolved in it, except at the end where the Jordan enters it; no fish or other animal can live in its waters, and it is hence emphatically called the "Dead Sea."

In Rájpútána, on the borders of the Bikanír desert, are some small salt lakes, the largest of which is the Sámbar Lake. This is a shallow depression, filled by the annual monsoon rainfall, (which here does not exceed twenty inches,) and then drying up. The salt obtained from it is an important article of commerce in Rájpútána. Another salt lake, yielding a salt of a different character, is that of Lunár in Berár. It forms a deep crater-like depression, and is thought to be of volcanic origin.

Lakes which have an outlet invariably contain fresh water; unless, like the Chilka Lake and other similar lagoons along the coast, they communicate directly with the sea, so that sea-water can enter them. There are but few instances of

I Possibly the drying up of the ancient lakes or inland seas, which, as Mr. W. T. Blanford has lately shown, once occupied Seistan and a large part of Persia.

Ix.]

ORIGIN OF LAKES.

127

natural lakes of fresh water in India; almost the only examples are certain little mountain lakes, such as that at Naina Tál and those below the Yaklá and Cholá Passes in Sikkim, lately discovered and described by Mr. W. T. Blanford. Beyond the snowy range, the Manasarovar and Rakhas Tál Lakes are larger instances of the kind. It is improbable that any of these are original rock basins; that is to say, hollows left in the disturbed rocks at the time when the mountain mass was upheaved. In some cases they appear to lie in hollows, worn by the friction of former glaciers in their rocky beds, and filled with water after the retreat or disappearance of the glacier. In other cases they are portions of old glacier valleys across which an old moraine forms a natural embankment or bund; and in others again, such as the Tso Moriri and the Pangong Lake in Rakshu and Ladákh, they appear to occupy portions of a valley, the drainage of which has been arrested by a mound of alluvial deposit, brought down by a mountain torrent from the lateral mountain ridge.

These remarks apply only to the lakes of the Himálaya and similar mountains elsewhere. Such great lakes as those of Canada, and those in East Africa on the Upper Nile, the Tanganyika, &c., may possibly be original rock basins, formed during upheaval : and those that cover Finland and North-Western Russia may be depressions in the old seabottom left as such when the country was elevated above the sea. It is, however, the opinion of Professor Ramsay, and some other eminent geologists, that the lakes of Finland and those of Canada, as well as the great lakes of the Alps, the lochs of Scotland and Ireland, and the beautiful mountain lakes of Cumberland, are all the work of ice during the Glacial period, the hollow basin now filled by water having been ground out of the solid rock, by the friction of enormous glaciers which once filled them, or rather by the stones, sand, &c., frozen hard in the bottom of the glacier, and dragged along with it over the surface.

The shallow swampy lakes that occur in certain river deltas, such as the salt lake to the east of Calcutta, are more

128

LAGOONS. SAND-SPITS.

[CHAP.

properly termed lagoons; and the same term is applied to those sheets of brackish or saltish water that occur on certain parts of the coast; of which the Chilka Lake in Orissa and the Púlicat Lake to the north of Madras are good examples. The former of these are portions of the delta lying between the river channels; and which the sediment deposited in them, year by year, has not yet sufficed to fill up to the ordinary dry weather water-level. In some cases, such as that of the examples cited, they are more or less salt, because they communicate by certain channels with the sea, so that salt water passes into them at every tide. The Chilka and Púlicat Lakes have been formed in a different way. They are separated from the sea by a ridge of sea sand, termed a sand-spit, and formed of sand drifted up the coast by the current noticed at page 48. To take the case of the Chilka: the sand accumulating along the shore of Ganjam and other more southerly parts of the coast, is gradually drifted northwards by this current, being added to by the sediment of every river that discharges itself into the Bay. At some former time, the sea must have washed the base of the hills that lie to the west of the Chilka; but this sea having become shallow by the sediment poured into it by the Mahánadi and the smaller streams from the interior, a sand-bank was formed by the coast current, tailing off from the southern extremity of the lake, until the lagoon behind it was almost completely enclosed. The sea alone could not raise this higher than the sand could be washed by the breakers; but as a part of it would be laid bare and dried by the sun at every ebb tide, the dry sand would be caught by the winds blowing from the sea, and raised in long mounds or sand-hills, rising twenty or thirty feet above the highest wash of the waves. In the course of time, various creeping plants which flourish on sand have taken root on the surface thus raised; the seeds being carried by the wind. These have fixed the sand, and by their decay have formed vegetable mould, fit for the nutriment of other plants, such as grass, the screw-pine, and the dwarf date-palm; and finally, as the spit has increased in width by further accretions on the seaward face, the older