SUyEDA AND BEACH TRAVEL
107
Suceda fruticosa and the plants which characteristically settle around it; it means that combined nitrogen does not long remain locked up in superfluous members of the plant, but gets early into circulation again.
  The Effect of Suaeda Bushes on Beach Travel. — By examining the relief of a beach carrying a natural vegetation of Suaeda bushes, and comparing it in detail with the distribution of the bushes, it is evident that the closest relation obtains between the two. The spots at which bushes are firmly attached to the beach tend, by the collection of shingle, to project above the general level, whilst the existence of these salients diverts the natural flow of shingle along lines which pass between the bushes. These lines of shingle-transport, or dynamic lines, tend to take the form of shallow gullies reaching from the crest via the gaps between the bushes to the lee margin, where the talus fans of their discharge accumulate.
   This condition is well illustrated on the Blakeney Bank, where the Suaedas occur in three discontinuous longitudinal belts or zones. In fig. 27 we give a typical strip of this bank, 50 feet wide and stretching from crest to marsh. The Suaeda bushes are plotted in black, and, by means of contour lines drawn for every half-foot from crest to marsh level, the principal features of the relief are exhibited.
  The contour lines show that two gullies start from the crest at points opposite the gaps in the upper Su^da zone, and that after traversing this zone they continue in the same way through the middle zone, and then die out below on the fan terrace between contours 3.5 feet and 4 feet. Towards the edge of this almost level terrace three little furrows are shown, corresponding to the spaces between the depots of accumulation of shingle which these gullies have brought. The edge of the fan below the terrace consists of shingle standing at a steep angle.
  We may note in passing the enduring permanence of these dynamic lines of shingle flow. It sometimes happens for a long series of years that no fresh shingle is thrown over at a certain part of the crest; all this while the gullies and the bushes maintain their original topographical relations, and whenever the moment arrives when shingle transport is re-