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FLOODS OF THE INDUS.

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a lake is formed behind the barrier; and continues to swell, until the water succeeds either in over-topping it, or in silently undermining it, when it at length bursts, and the pent-up torrent, suddenly set free, rushes downwards once more with overwhelming impetuosity and power.

The following graphic account of a great flood of this kind, which occurred in the beginning of June 1841, and was witnessed by Asharaf Dhán of Torbela, is given by Major Abbott in the words of the narrator: "At about 2 P.M. a murmuring sound was heard from the north-east among the mountains, which increased until it attracted universal attention, and we began to exclaim 'What is this murmur? Is it the sound of cannon in the distance? Is Gandgarh1 bellowing? Is it thunder?' Suddenly some one cried out The river is come!' and on looking I perceived that all the dry channels were already filled, and that the river was racing down furiously in an absolute wall of mud, for it had not at all the colour or appearance of water. They who saw it in time easily escaped; they who did not, were inevitably lost. It was a horrible mass of foul water, carcases of soldiers, peasants, war-steeds, camels, tents, mules, asses, and household furniture-in short, every item of existence jumbled together in one flood of ruin; for Raja Golab Singh's army was encamped in the bed of the Indus at Kulai, three kos above Torbela, in pursuit of Paindu Khan. Part of the force was at that moment in hot pursuit, or the ruin would have been wider. The rest ran: some to large trees, which were all soon uprooted and borne away; others to rocks, which were speedily buried beneath the waters. Only they escaped who took at once to the mountain-side. About five hundred of these troops were at once swept to destruction. The mischief was immense hundreds of acres of arable land were licked up and carried away by the waters. The whole of the Sisú-trees which adorned the river's banks, the famous Bargah-tree of many stems, time out of mind the chosen bivouac of travellers, were all lost in an instant."

So spelt in the original. Query, Gandaka, Sans., one of the names of the rhinoceros.

120

EXCAVATION OF VALLEYS.

[CHAP.

On this occasion, according to Major Montgomerie, the cause of the flood was a landslip in the Gilghit valley. The valley was blocked up by an enormous mass of earth and rock that had slipped down from the side of a mountain; and a lake was formed behind it, which is believed to have been 800 or 900 feet or more deep. At last the barrier gave way, and the whole mass of pent-up water was suddenly discharged down the valley.

Another great flood, arising apparently from a similar cause, occurred in August 1858.

In describing the Mahánadi in the previous chapter, I observed that the valley in which each stream flows is the work of its own waters. It is in the Himálaya that we have the grandest examples of this kind of river action; and this will be the most convenient place to describe it somewhat more in detail. In the loftier valleys, in the neighbourhood of the permanent snows, glaciers are powerful agents in eroding and excavating the rocks over which they pass. The masses of rock which are carried down by the ice stream, firmly frozen in the ice, are dragged over the bare rocks of the sides and bed of the glacier, grooving them and grinding them down with perfectly resistless force. The sand and mud so produced are carried away by the stream which issues from the end of the glacier, gushing out from an ice cavern at its foot, turbid with glacier-mud. In former times the Himálayan glaciers extended far below their present limits, and they have performed no unimportant part in scooping out the great river valleys. In the Tísta valley in Sikkim, glaciers do not now extend below 14,000 feet, but traces of their former work are still visible down to 6,000 feet above the sea-level; while in the Kángra valley in the North-West Himálaya, similar indications are met with as low as 3,000 feet above the sea.

But the river itself is also a powerful excavator. Rushing down steep slopes with a high velocity, it has power to roll along pebbles and even large masses of rock, grinding them against each other and over its rocky bed, and insensibly wearing down the latter, however hard may be the rock that

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FORMS OF VALLEYS.

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forms it. In a hard rock the river excavates a gorge, with precipitous sides, very narrow, but sometimes of great depth. Such is the remarkable gorge at the junction of the Sutlej and Spiti rivers (Fig. 17). Where the rocks are less hard and stubborn, the sides of the valley become more sloping under the action of frost and the atmosphere. The surface of the rock is splintered and falls, and the fallen mass is gradually ground up and borne away by the torrent.

Rocks differ extremely in their power of resisting decomposition. In certain cases it would seem that, after exposure for centuries to the action of rain and frost, they present the same unyielding surface, unchanged in form and texture. In other cases frost and rainwater, aided by those chemical

1 From a photograph by Messrs. Bourne and Shepherd.

122

LANDSLIPS.

DETRITUS.

[CHAP. constituents of the atmosphere called carbonic acid gas and oxygen, not only disintegrate the whole superficial mass of the rock, reducing the hard stone to the state of clay and gravel, but carry this action far into the heart of the mountain. Where this has taken place, the excavation of the valley goes on rapidly. From time to time, especially after heavy rainfall, enormous masses of earth and rocks, becoming saturated with water, slide down the mountain side, carrying everything before them; and after blocking the valley for a time, are carried away by the ceaseless action of the stream. In this way, as was pointed out above, are caused some of those sudden floods of which two extraordinary examples were quoted.

In a country such as British Sikkim, where the rainfall is great, the rocks easily decomposed, and the forest growth exceedingly luxuriant, the form of the mountain slopes is almost entirely due to landslips. In the neighbourhood of Darjiling, after each heavy fall of rain, the hill-roads are generally interrupted in many places by little falls of this kind; and sometimes the mountain-side, to a height of 3,000 or 4,000 feet, is seen freshly exposed, the whole of the surface with the forest that covered it having been precipitated into the valley below. The accompanying view of the Ganges at Derali,1 will serve to give the reader who has never visited the mountains, some idea of an ordinary river valley in the Himálaya.

By these various agents, frost, rain, carbonic acid, and finally gravitation, the original hollows and inequalities of the newly-raised mountain mass have been connected, and further carved and excavated, so as to form a complete system of valleys, separated by mountain ridges. The materials carried away in the process have been partly deposited in the original hollows, as great gravel deposits, such as are seen everywhere in the valleys of Ladákh, and that through which the Sutlej has excavated its valley in the Tibetan province of Guge; but the greater part, when ground down so fine that they could be carried out into the 1 From a photograph by Messrs. Bourne and Shepherd.

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ALLUVIAL PLAINS. WATERFALLS.

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plains, have been spread abroad by the rivers, forming the arable lands of the Gangetic plains. These plains then are formed of the waste of the mountains, and though they themselves have also been wasted, and are still being worn down and their materials borne away and deposited in the ocean, they receive on the whole more than they lose, and the greater part of this is derived from the Himalaya. But all the hill tracts of India are subject to the same process of degradation, and so in various degrees are all mountains whatever.

Amid the endless variety of feature presented by rivers, in their course through hilly countries, none is more striking and impressive than their falls. A fall occurs whenever, owing to some peculiarity in the geological structure of the country, there is a sudden precipitous descent of the channel, over which the whole body of water is precipitated to a lower level. Among the best known and largest waterfalls in the Peninsula of India are the falls of the Saravati river in Kanara, those of the Yenna in the Mahábleshwar hills, those of the Káveri in Maisur,