Section IV comprises an analysis of the salinity, exchangeable Na and Ca, and the moisture factors of salt marshes in Norfolk. Moisture is not: a significant factor. The exchangeable Na behaves independently of the total chloride and it is suggested that the ion may be bound in the colloidal clay soil. Total chloride falls in the spring in the surface layers and this probably encourages seed germina-tion. The upper and lower marshes contrast strongly in the summer as to surface salinity. Section V describes the algal vegetation, 16 communities being recognized. This vegetation is compared with that from other British salt marshes.