DYNAMIC LINES
109
mechanism was once more brought into play, the line of travel was that followed on the previous occasion.
   Apart from the gullies, which pick out the gaps in the successive zones of bushes and link them together, the bushes tend to raise the beach level on their crestward side by obstructing the movement of and holding such shingle as reaches them—clearly shown in the profile represented in fig. 29.
This raising of level is generally accompanied by a partial burying and prostration of the shoots, and these in their turn respond by active rejuvenescence in the manner already described (p. 104).
In this connection it may be pointed out that the more a Suaeda bush is shingled over the better adapted does it become to resist the passage of shingle. For by continual development of fresh laterals the total number of shoots standing vertically, per unit of area, is greatly increased, with corresponding improvement of the mechanism as an accretor of shingle. Where shingle is mobile, main axes or branches are not permitted to project for indefinite periods above the ground. Consequently a bush high up on the beach, though lineally descended by vegetative continuity from a seedling dating back perhaps
SECTION OF FAN
MARSH FLOOR
Fig. a8.—Diagram showing Permanence of Dynamic Lines after a Long Interval
  The old gully, which passes between the Suseda bushes and which in 1897 discharged the fan marked "old”, served again in 191a to bring new shingle to the selfsame spot. The smaller figure below is a section showing the newly brought shingle overlying the old: note that the edge of the former lies at a steeper angle than the latter. The small circles on the old fan are young Suaidas that have established during the period of dormancy.