i 4 8 LOCAL EFFECTS OF INUNDATIONS. 



valleys which undulate the stratified rocks, seizes upon the imagina- 

 tion, and we re-examine all our notions of the origin of these great 

 surface-undulations. The fissures in the limestone rocks which stop 

 and swallow up the gathered streams, are analogous to those longi- 

 tudinal valleys beneath the escarpments of the Oolites and the Chalk 

 by which the rivers are turned at right angles to their earlier course, 

 while the lower edge of the fissure corresponds to the escarpment 

 itself, with its new system of denudations. 



To see these rain and time-ploughed furrows winding in uncertain 

 directions over the horizontal limestones on the hill-top, like a slow 

 river in a level plain, but running a straight downward course on the 

 slopes, like a stream descending from its parent mountains, is enough 

 to impress on every beholder a secure conviction that the excavation 

 of many valleys must be explained upon similar principles ; that, as the 

 feeble currents of descending rain, aided by long time, have been 

 sufficient to plough their little courses, so the greater action of existing 

 streams has been sufficient to work out their actual channels, though 

 the excavation of the broad valleys in which they run, may have been 

 accomplished by more violent and voluminous waters. 



Effects of Inundations. The slow but incessant action of rain 

 beating perpetually on the hard and the soft surface of the earth, and 

 removing grain by grain the materials loosened by the expansive 

 agency of frost, and by moisture and chemical changes, may, in a long 

 series of years, be more important in its effects than the violent water- 

 spout, or the ravaging inundation of a bursting lake. Yet the effects 

 of water-spouts are tremendous in countries composed of easily de- 

 structible or unequally indurated materials. A waterspout which fell 

 above Kettlewell, in Yorkshire, committed terrible ravages in the 

 narrow valley of the Wharfe, near Kettlewell and Starbottom. On 

 the sides of the mountains in Cumberland, traces of these visitations 

 seem utterly ineffaceable ; and the memory of the sudden bursting of 

 the Peat Bog, above Keighley, will long be preserved in the valley of 

 the Aire. The floods which rushed simultaneously from the Cairn 

 Gorum and other mountains, in August 1829, over 5000 square miles 

 of Aberdeenshire and other counties, were of prodigious fury, removing 

 hundreds of tons of large stones, whole acres of woodland, and almost 

 hills of earth. The desolating effects of the bursting of the ice-dam 

 which had formed the temporary Lake of Bagnes, are matters of 

 history. The moving mass of water, mud, and monstrous rocks, which 

 swept with violence down the valley of the Dranse, carried away 

 forests, houses, bridges, cattle, and men. In six hours and a half it 

 passed through an unequal and irregular course of forty-five miles, till 

 lost in the Lake of Geneva. 



Glaciers. Glaciers are likewise to be enumerated among the 

 powerful agents by which the higher lands are wasted, and materials 

 provided for raising the lower. As the summer heat melts every 

 year the lower portions of these long winding rivers of ice, and the 

 heated ground thaws, the gathering water dissolves their founda- 

 tion, and the whole mighty mass of snowy ice slides slowly down- 



