SECTIONAL TRANSACTIONS.— C. 411 



seaward side. These interdigitate as a result of former conditions of marine 

 transgression and regression. The work of the Fenland Research Com- 

 mittee since its foundation in 1932 under the Presidency of Prof. Sir A. C. 

 Seward, F.R.S., has been the correlation of the history of formation of 

 these deposits with the evidence of geologists, archaeologists, botanists and 

 other specialists with as many as possible other events of local post-glacial 

 history. For the outlines of the conclusions of this Committee see articles 

 in the Scientific Survey, by Godwin, Clark, Phillips and others. 



Dr. W. A. Macfadyen. — Foraminifera from the post-glacial Fenland 

 deposits. 



The Foraminifera include an indigenous fauna, and derived specimens 

 from the Cretaceous and Jurassic. Derived Jurassic specimens are only 

 occasional, and seem to originate close to where they are now found. The 

 Chalk forms are a constant feature of the silts, and are considered to have 

 been brought up the water channels from the sea coast, from outcrops of 

 Chalk or Chalky Boulder Clay. In the buttery clay they are correlated with 

 the subsidiary silt content. 



The indigenous Foraminifera include no extinct forms, and indicate no 

 difference in climate from that of the present day. They may be used as 

 a scale of the salinity, which varied from estuarine to practically fresh water. 

 The silts were characteristic of estuarine conditions, while the clays were 

 apparently deposited in lagoons, into which estuarine water occasionally 

 overflowed. 



Different species of a genus of Foraminifera exhibit varying tolerance of 

 admixed fresh water, and this is here most clearly exemplified in the genera 

 Quinqueloculina, Trochammina,, Bolivina, Lag^na, Discorbis, Nonion and 

 Elphidiiim. Nonion depressulus and Rotalia beccarii can flourish in water 

 that is practically fresh, and the species of Trochammina appear definitely 

 to prefer a somewhat brackish habitat. 



Mr. H. L. P. Jolly. — Levels and bench marks. 



The bench marks of the Ordnance Survey are habitually placed upon 

 structures which bid fair to be the most stable. Hence the great sub- 

 sidences in the fen levels due to drainage are not recorded by any of the 

 re-levellings which have been carried out. For much of the area there 

 exist records of three levellings dated approximately 60, 30 and 10 years 

 ago. In general, these show no appreciable changes wherever the bench 

 marks are on buildings situated more than 20 ft. above mean sea level ; 

 situated, that is, on outcrops of Cretaceous or older rock and not on the 

 alluvium. Some bench marks have of necessity been placed in the drained 

 districts and these, being generally on houses or other brick structures 

 placed on or near an artificial bank, have shown subsidences of from nothing 

 to I ft. or even nearly 2 ft. Such measurements serve, however, only to 

 give precision to what is otherwise very patent to the eye, for the houses 

 bear much evidence of subsidence in the shape of cracks, tilting or even 

 collapse. This is especially the case where, as often, the house is built 

 as close to the bank as possible, so that one end of it rests on the bank and 

 the other on or near the fen. The Middle Fen Bank at Prickwillow has 

 a colony of houses, all of which show distortion of some kind. The 

 maximum subsidence shown there by Ordnance Survey bench marks is 

 0-74 ft. between the years 1870 and 1901 and a further 10 ft. between 

 1 90 1 and 1925. Evidence of soil subsidence beyond that recorded by the 



