. Karakoram and western Himalaya 1909, an account of the expedition of H. R. H. Prince Luigi Amadeo of Savoy, duke of the Abruzzi. sintegrationis so continual and on so vast a scale that the general aspect of thevalleys must perforce change at many points every few years. Tracesof avalanches are everywhere visible, signs of ancient or recent cata-clysms, boulders polished to a shining red-brown surface by time andthe action of water, lying alongside of huge blocks, whose clear-cutfractures seem of yesterday, at the feet of rock walls torn with freshgashes. Sir Martin Conway attiibutes this rem
. Karakoram and western Himalaya 1909, an account of the expedition of H. R. H. Prince Luigi Amadeo of Savoy, duke of the Abruzzi. sintegrationis so continual and on so vast a scale that the general aspect of thevalleys must perforce change at many points every few years. Tracesof avalanches are everywhere visible, signs of ancient or recent cata-clysms, boulders polished to a shining red-brown surface by time andthe action of water, lying alongside of huge blocks, whose clear-cutfractures seem of yesterday, at the feet of rock walls torn with freshgashes. Sir Martin Conway attiibutes this remarkable decay of the rockssolely to climatic causes—drought and swift and extreme changes of 94 Chapter VII. temperature. But surely a great part must be played by the absolutelack of any layer of vegetation which would protect the live rock fromthe direct action of excessive heat or frost, and by absorbing the watersto hinder them from bursting in sudden torrents down into the valleys. The bed of the valleys alters its shape incessantly. TUnremittinglythe river gnaws, wears down and digs out its bed, and shifts, rolls and. THE IXDUS JUST BELOW THE MOUTH OF THE DKAS. diags down millions of tons of mattei, which it deposits wherever thecurrent slackens above a narrow gorge or pile of boulders, only to movethem again once the obstacle is removed or cut thiough. The lavers of detritus and sediment sometimes attain a thicknessof 1,000 feet or more. The sedimentary deposits are of every speciesand variety : banks of the finest and purest clay, pebbles, agglomeratesof every variety and period. They usually take the form of terracescut steep down to the river. They are not, however, invariably at thebottom of the vallev, the remains of ancient sedimentary depositssometimes cUnging to the walls up to a great height. Thomson foundcla) deposits between 1,000 and 2,000 feet above the stream, as highup as the brow of the chffs along the valley; and Schlagintweit found TIr Indus Valkv. 95
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