✓ 
22 PELOPHILOUS FORMATION OF LEFT BANK OF SEVERN ESTUARY. 
DISCUSSION OF TABLE II. 
It is clear that one result of the marked difference in level be- 
tween the zones in this formation will be that the number of 
times they are submerged and the duration of this submergence 
will be very markedly different. It is only possible to give 
approximate figures, but calculating from tide tables, coupled 
with measurements made at the time of full tide on a calm day, 
I estimate that during 1910 the Festuca zone at Portishead was 
submerged by 40 tides, the Sclerochloa zone by no, and the 
Salicornia zone by 150. The duration of submergence would also 
of course vary in about the same proportion. 
This would lead one to expect that the Salicornia zone would 
have the least opportunity of having its salt content removed by 
drainage after rain, and a reference to the Table shows that the 
percentage of chlorine never falls so low in the Salicornia zone. 
The minimum readings for the zones are as follows — 
Salicornia zone .. . ... ... 0*21 % 
Sclerochloa zone ... ... 0*09 % 
Festuca zone ... ... ... 0*03 % 
If minimum results only were considered it would appear sur- 
prising that the whole formation was so definitely halophytic ; 
thus the normal chlorine content of the reclaimed pastures is 
o'02 %, and Warming states 1 that in a rapidly drying clay such 
as is present here 1 % sodium chloride is required to expel all 
plants but halophytes (1 % N a CI. would be equivalent to o*6 % 
chlorine). 
It is thus surprising to find the Festuca zone so markedly 
halophytic until the other chlorine figures for this zone are con- 
sidered, when it will be seen that the maximum figures for salt 
content appear in this zone at positions removed from the margin. 
The percentages of chlorine rises to such a figure as 1*34 % 
during a spell of dry weather ; for April 1st, 1910, had been 
preceded by an absolutely dry fortnight, and the total rainfall for 
the previous month was very small. This result is to be accounted 
for presumably by two factors, first the inefficient drainage 
preventing the water from the high spring-tides running away 
freely — the zone had probably been submerged about seven times 
without any subsequent rainfall — and secondly by the salt being 
retained in the upper four inches of the soil by the action of sur- 
face tension and evaporation. This same zone after heavy rain 
will show a chlorine content, probably in the neighbourhood of 
0*2 % — 0*4 % (see readings for Dec. nth, 1909), while under ex- 
ceptional conditions for drainage in a time of low tides it may 
fall even lower (see readings for January nth, 1910). 
The distinctive difference between the three zones as regards 
halophytic factors seem then to be connected w 7 ith drainage 
1 Warming, loc. cit. p. 218. 
