Reaction and Succession in Relation to the Plant Covering . 4 1 5 
The Organic Content . 
The youngest bank has a very low organic content, under a half 
per cent., whilst again the eighth lateral shows the extreme condition with 
an average of over 22 per cent., and there is falling off in the older laterals. 
Here, then, it is quite evident that the increasing organic content 
accompanying increasing age is a feature of the lateral shingle banks 
as well as of the dunes. That the diminished organic content of the oldest 
Text-fig. 5. Graph showing relation between percentage carbonate content of the soil of the 
crest of shingle laterals and their age as indicated by their positions in the shingle system. 
laterals is correlated with their lower level is borne out by the exceptionally 
high organic content shown by the soils of the ‘ high elbows ’ of both 
laterals VIII and VII. In the former the organic content may be nearly 
29 per cent., and in the latter nearly 15 per cent, as compared with about 
12 per cent, and 4 per cent, as the respective observed maxima for 
the lower parts of the crest. 
The Hydrogen-ion Concentration (cf. Tables XI and XIII , Appendix ). 
As is to be expected from the foregoing considerations, the reaction of the 
soil of these laterals exhibits an increasing acidity with age, which attains 
its maximum on the high elbow of Bank VIII with a p. H. of 5-9. The 
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