Reaction and Succession in Relation to the Plant Covering. 4 1 3 
densest growth of Silene maritima and A. peploides, with the addition in 
particular of Sonchus arvensis v. angustifolius , $ estuca rubra , three isolated 
patches of Convolvulus soldanella and two of Tussilago Farfara. The latter 
is often regarded as characteristic of stiff clayey soils, but its absence from 
many lighter types is very probably an outcome of their poverty in mineral 
salts and acid tendency. Unless it be the conditions associated with a more 
or less neutral reaction that determine the occurrence of T. Farfara its 
presence here demands explanation. 
Organic Content \ Carbonates , and p. H. 
In order to appreciate the significance of the data regarding the 
organic content, carbonate content, and hydrogen-ion concentration, it 
is necessary to appreciate that, just as the main dune ridge, which marks 
the oldest range with marked accretion, is the highest, so too the shingle 
laterals develop to a maximum, after which they undergo a flattening pro- 
cess partly perhaps the outcome of wave action, but largely the natural 
process of ‘ settling ’ which manifests itself chiefly in the replacement of the 
convex crest by a flat one. The highest level reached by laterals is at their 
L-shaped distal end, which forms a high elbow here, although only reached 
by the highest tides during exceptional storms ; the same flattening of 
the profile is to be noted. 
As a consequence of this lowering of the level with age, the oldest 
lateral banks share in common with the younger the fact that they are more 
frequently tide-covered than those of intermediate age ; it is to this that we 
must attribute the attainment of the most extreme conditions associated 
with increasing age on the Watchhouse bank and high elbows. 
The Carbonate Content. 
The data in Table XI, Appendix, and the appended summary 
Table XII, show that the total carbonates are highest in the youngest 
lateral XX and fall to their minimum in laterals IV to VIII, again rising 
slightly in I and III. 
Table XII. 
Summary of Data for Crest of Laterals. 
(Averages of all estimations.) 
Youngest bank = XX ; oldest = I. 
XX. 
XVII. 
XVI. 
XII. 
VIII. 
VII. 
IV. 
III. 
•I. 
Av. loss on ignition % 
0.486 
0.32 
— 
7.12 
22.45 
5-5 2 
2-39 
2.64 
3 ,I 9 
,, total carbonates % 
0.813 
0-16 
— 
0.103 
0.03 
0.03 
o-oo 
0.006 
0.015. 
,, P.H. 
7-59 
7.22 
7.0 
67 2 
6.38 
6-59 
6-96 
6-86 
6.90 
Here then, too, as on the older dunes, we see the effect of leaching 
clearly marked. In the case of Bank VIII the two spots on the high elbow 
Gg 
