Waves of sand and snow and the eddies which make them . ws through the Durrant estate, thereare some reaches where the bottom is covered withclean sand. In one of these the course of thle:stream is perfectly straight, and it flows betweenperpendicular banks about seven feet apart. Thedepth was 37 5 inches, and the current flowed atthe speed of 0-85 foot per second. The sand wasin ripples of the form just described—, withbroad and nearly flat crests, and were not onlyfairly regular in wave-length but stretched almostthe whole way across the stream in continuousridges at right angles to the
Waves of sand and snow and the eddies which make them . ws through the Durrant estate, thereare some reaches where the bottom is covered withclean sand. In one of these the course of thle:stream is perfectly straight, and it flows betweenperpendicular banks about seven feet apart. Thedepth was 37 5 inches, and the current flowed atthe speed of 0-85 foot per second. The sand wasin ripples of the form just described—, withbroad and nearly flat crests, and were not onlyfairly regular in wave-length but stretched almostthe whole way across the stream in continuousridges at right angles to the banks. Forty-sixconsecutive ripples had an average wave-length of6 inches, and an average height of approximately03 5 inch. I saw these in 1911, fifteen years afterI first observed the same type of sand-ripple inwinding channels. Not until I saw the regularityof the ridges in the canalized stream did I realizethat so slow a current could produce such regularripples. I had noticed, however, something of thesame kind with regard to water-waves. I have. o tijC a, a, S^:m^4 26; RIPPLE-MARK AND CURRENT-MARK 269 pointed out elsewhere ^ that a winding course isinimical to the formation of river waves of fixedposition and size, because the lower layers of waterdo not flow in the same vertical plane ^ as theupper, so that there is always a tendency to set upwhirlpool motion instead of wave motion. The presence of bottom currents crossing thedirection of those of the surface is likewise inimicalto the formation of transverse sand-ridges. I was at first much puzzled by the fact thatalthough the sand ripples in the Bourne were sonumerous, regular, and well-developed, theyappeared to be scarcely stirred by the water. Iput sticks into the sand at the edge of the littlecliffs, and after a quarter of an hour I found thatthe cliffs had not moved. Now, the sand ripples inthe Branksome brook had moved half an inch perminute under the action of a somewhat slowercurrent. I came to the conclusion
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Keywords: ., bookcentury1900, bookdecade1910, bookidwavesofs, booksubjectwaves
