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Show !36 ACTION OF water above the level of the sea, unless on t~e ahf surd supposition that the ~ater .ran up one stde o the mountain for no other Imagmable p~.Irpose than that it might run down the other-that It ~cted contrary to the law of gravit~tio~ on one side of t?e summit, just in order that It m1ght the more. readily and effectually obey that law on the other ~Ide. . Even-in plainer cases than that-tho~e m 'Yhtch there is only a gradually inclining.dell~ Wit~ a nvulet meandering along-we cannot give the nvulet the merit of making the dell, at least not out of the hard strata of primary rock; because, unless. we have the dell at the beginning, we cannot ~xplam why there is a rivulet there; even rivulets, If they are to PA permanent, must have permanent c~uses ~ antl, unless where there is a spring supplied with water from a store farther up, the slC!ping si~es of the dell are necessary to provide th~ nvulet wt~h. water. In rivers of l0nger course, that IS more ~tnkmg. Take, for instance, the Thames; the quantity of wa~er th~t rises up in the springs, ~houg:h .much .magmfi~d m the pictorial representatiOns, IS m reahty consld.erable : but look at the distance to the sea, ~nd thmk whether instead of that infant stream havmg excavated th~ goodly valley of which it is now the wealth and the ornament it must not have been evaporated before it could have reached Windsor or even Ox-forTdh. at a river can cut deeply even ·m t o h d v~ry ar strata is proved by many instances ; but 1n those instances there are always slopes above ~o s~n~ down in a flood during rains, that water which, If 1t fell on level gr~und, would sink into the earth, and not form any flood at all : so that there. could be no cutting through even the softest matenals. These cuttings are, in genera~, the seconda~y stra.ta, or even collections of rubbish; and there ~s perhaps no instance of a dell formed by the 3:ctwn of water wholly in the solid granite, though m many places RIVERS. 237 there are little notches. The cutting of the rubbish may go on very rapidly, so that a large excavation may be made in a year, or even a day; but the solid and seamless rock is quite another matter, and we find that even a considerable river, with the assistance of a valley every way well adapted for the producing of powerful floods, makes but little impression on such strata in the course of ages. The North Esk, which discharges its waters into the British ocean, a few miles to the northward of Montrose, and the Isla, which flows by the castle of Airlie, from the southern slope of the Grampians to the valley of Strathmore, are perhaps two of the most striking instances of rivers cutting the soil that are to be met with in Britain. Both rivers drain mountain valleys, the sides of which are steep, and the autumnal rains fall very heavily on both. There is no lake on the Isla to regulate the waters when the rains fall, and on the North Esk there is but one small one (Loch Lee), which is far in the mountains near the source of the river, and has little influence on the whole stream, because a great part of the water of floods comes into the channel lower down. · Each of those rivers has cut a dell, or den, several m~les in length, and very deep in proportion to its Width. But gravel and red sandstone (which in those places is a soft crumbling stone, together with p~dding-stone, very wea~ly cemented) are the principal matters through whiCh these rivers have cut. Even now the cuts which they have made are little mo~e than sufficient for containing the flood water dunng the rains. Gannachie bridge is thrown across the dell of the Esk, among the very pictu, resque scenery at " The Burn;" and though, in common states of the river, the roadway on the bridge be a~ least fifty feet above the water, the floods rise UsoL lngh Gth at a tall man of the villarre locally named b) ang annachie," could reach over the parapet |