Waves of sand and snow and the eddies which make them . circumstances to which atten-tion should be chiefly drawn are the steep gradientof the river, or estuary, and the presence of a sidechannel into which the flood tide is diverted atits commencement. The sand or shingle spits outside the estuariesof the Mawdach, Findhorn, and South Esk preventthe flood tide there from finding an alternativechannel. Lower down the estuary of the Severn, wherethe Severn railway tunnel has been made, thereis a rocky shoal called English Stones, which com-pels the incoming tide to stem the current of theebb and
Waves of sand and snow and the eddies which make them . circumstances to which atten-tion should be chiefly drawn are the steep gradientof the river, or estuary, and the presence of a sidechannel into which the flood tide is diverted atits commencement. The sand or shingle spits outside the estuariesof the Mawdach, Findhorn, and South Esk preventthe flood tide there from finding an alternativechannel. Lower down the estuary of the Severn, wherethe Severn railway tunnel has been made, thereis a rocky shoal called English Stones, which com-pels the incoming tide to stem the current of theebb and follow the principal channel under theright bank. Thiis the reach of the Severn im-mediately above the English Stones resembles theestuaries of the Mawdach and South Esk. Thegradient of the channel in this part of the Severnis also much less than at Severn Bridge. A littlehigher up than English Stones is the shoal calledDun Sands. Hearing that this, unlike theWaveridge, was often in large waves, I went downby boat next day, April 27th. I passed many. P 307 SAND-WAVES IN TIDAL CURRENTS 309 sandbanks in that part of the Severn below thebridge where the gradient of the channel is steep,all of which had dried out with a smooth Dun Sands, however, was all in large sand-waves. A series of fifteen had an average lengthof 37 feet 8| inches, and an average height ofI foot 11-22 inches, the length being, therefore,19-49 times as great as the height. The meandifference between the lengths of successive waveswas 26-4 per cent, of the average length, and theniean difference between successive heights was37-7 per cent, of the average height. These ridgeshad somewhat undulating crests and sinuous fronts,and in rriany places pools of water are left in thetroughs, where, my boatmen told me, salmon aresometimes impounded. This state of things is nodoubt due to a current which sets across this partof the shoal after the higher south-west part un-covers during the ebb. In some places
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