Swift water dives under slow, and sorts sand from gravel
Red-chalk current study: fine sand near the fall, coarse gravel beyond, keyed a, b
A red-chalk leaf, drawn upside down, captioned as a study of a water current and keyed with the letters b and a. The note explains that the faster line of water breaks through the slower and drives itself beneath it. It then describes how the stream sorts the bed: the sand nearest the impact of the falling water is the finest, while the coarse gravel lies farther from the blow.
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Faster water breaks and dives beneath slower water
The line of water with greater movement breaks the line of lesser motion and drives itself beneath it. The current is traced along the lettered channel from b to a.
Falling water sorts fine sand from coarse gravel
The part of the sand nearest the percussion of the falling water is finer than the rest, while the coarse gravel comes to rest farther from the blow. The impact grades the bed material by size and distance.