TRANSACTIONS OP SECTION K. 563 



the landward slope. (2) By the percolation of sea-water at high tide, whereby 

 shingle at the foot of the landward slope is dislodged by gushes of water, 

 with the result that the bank is constantly undermined and shingle descends 

 from above. (1) is of special importance in the case of low banks on exposed 

 coasts, (2) where the crest of the bank stands high above tidal limits. 



Banks in which these processes are operative offer conditions analogous to 

 those obtaining on wandering sand dunes. Whilst some parts of a shingle bank 

 are thus rendered active, others remain passive for the time being — a condition 

 usually indicated by the presence of lichens, and of certain angiosperms which 

 do not gain a footing whilst the mobile phase persists. The passive phase is 

 well illustrated on parts of the Chesil Bank and by the lateral banks (or land- 

 ward hooks) at Blakeney, Hurst Castle, and elsewhere. On these, as a rule, 

 the vegetation shows a definite succession — analogous to the resting phase of a 

 sand dune. 



The question of the origin of a soil occupying the interstices of the shingle 

 is an all-important matter for the vegetation covering. In part, the soil is 

 formed by lichens and higher plants, the products of whose disintegration may 

 be traced to the deeper layers. This source is supplemented by tidal drift left 

 by the sea and scattered over the bank by the wind. But the most important 

 source of all appears to be the drift on the landward side of the bank derived 

 from the salt marshes which are commonly present here. This drift accumulates 

 at the foot of the landward slope in enormous quantities, and is incorporated 

 by the shingle in its slow landward progress. A mobile shingle bank flanked 

 by a salt marsh is a remarkably perfect mechanism for mingling this humus 

 with the shingle. The extreme sterility of many stretches of shingle is doubt- 

 less referable to some defect in the working of this mechanism. Whether the 

 drift be withheld, on the one hand, or the onward creep of the shingle (whereby 

 the drift is assimilated), be arrested, on the other, the result will be the same 

 — unless, of course, the bank is so far advanced in its succession as to be self- 

 contained so far as soil is concerned. 



A common cause of sterility is the reclaiming (by dyking) of the salt 

 marshes on the landward side, the immediate result being a cessation of the 

 supply of drift owing to the exclusion of the tides from the marshes. Inci- 

 dentally it may be noted that such starved banks are apt to retrograde and 

 exhibit an unusual degree of mobility, so that shingle is often spread over the 

 marshes on a large scale. 



Another cause of sterility is the isolation of portions of a shingle bank 

 from its humus supplies by the accretion of sand dunes. 



Perhaps the most unexpected feature of the shingle bank as a habitat for 

 plants is the rich supply of water with which it is provided. Apart from the 

 halophytes which tend to creep up the bank from the salt marsh, the majority 

 of the plant population is non-halophytic. The water, at any rate in the upper 

 zones,, is evidently fresh, or nearly so, and its presence requires elucidation. 

 During the current year, notable for its prolonged drought and high tempera- 

 tures, no drought-effects have been recorded on any of the shingle banks under 

 observation. 



In conclusion it may be remarked that a shingle bank is a complicated 

 structure bearing numerous different types of habitat which it will be con- 

 venient to discriminate by a separate terminology when the vegetation comes to 

 be more fully studied. 



2. The Swiss National Park and its Flora. By Professor C. Schroter. 



In Switzerland there are now four organisations working for the protection 

 of Nature— the Commission for the Protection of Natural and Prehistoric Monu- 

 ments; the Society of Swiss Foresters; the Swiss National Trust; and the 

 League for the Protection of Nature (' Naturschutzbund '), which has in two 

 years attained a membership of eleven thousand. 



Up to the present the following results have been obtained : — 

 1. Laws for the protection of plants have been passed in the majority of 

 cantons. 



o o 2 



