RATES OF ACCRETION
201
  Example 2.—Low marsh which in 1910 bore only a thin scattering of Salicornia annua (Marsh Samphire), Fucus limicola, and a few plants of Aster Tripolium. Since 1910 the vegetation has rapidly increased, until at the present time (1917) the Salicornia has reached maximum density and Asters are everywhere abundant. Other halophytes are also making their appearance. The marsh is covered by almost every tide, say 700 a year. Rise of level in 2 years 5 months, 2.5 inches under Salicornia, 3 inches under Fucus limicola. At the latter rate the rise would be 1 foot in 9! years. This is the largest result yet obtained.
  Example j.—Salicornia-Pelvetia marsh, covered by all spring tides (240 tides a year) and in the centre by the higher neap tides as well (making about 600 tides a year). Determinations were obtained at stations every 10 feet along a line crossing the long axis of the marsh at right angles, i.e. from bank to bank.
   The rise in level after 2 years ranged from 0.2 inch at the edge to 1-1.25 inches at the centre, the intervening stations, according to their position, giving readings intermediate between these extremes. At these rates of silting the rise in level ranged from 1 foot in 120 years, at the edge, to 1 foot in 19 years at the centre. The distribution of silting here is in conformity with the fact that young marshes are generally concave (i.e. slope down gently to the creek), whilst old high saltings are practically dead level.
   We are indebted to Dr. M. C. Stopes for organizing the series of accretion stations (in August, 1914) in Example 3, and to Dr. E. J. Salisbury and Mr. B. K. Hunter for measuring up the results (in August, 1916).
   The above, and other preliminary results that have come to hand, all point to the importance of the number of tidal immersions in determining the amount of silt deposited. Whilst this is no doubt the most important factor, we are impressed with the high efficiency of the embedded Fucus limicola in promoting accretion. In Example 2 (and other cases bear out these results) ground with Fucus grew 0.5 inch more in 2 years 5 months