550 F. Hardy — Mineral Com/position of Fenland Silt. 



in the silt sample is 0'112 per cent, which corresponds to about 

 0'28 percent of apatite. Frequently in soils (especially in peat and 

 other soils rich in humus), phosphorus probably also occurs as 

 organic phosphorus compounds. In the case of the silt under 

 consideration, the possibility of the presence of organic phosphorus 

 is negligible, since the silt contains only 0"034 per cent of nitrogen 

 (corresponding to about '0'48 per cent of humus). Hence we may 

 safely assume that the only phosphorus compound present in the 

 silt is the mineral apatite. The percentage of phosphate (0'112 per 

 cent P2O5) is of average amount for a soil ; the range for typical 

 soils being between 0'06 and 0"20 per cent PjOg. 



(D) Other Mikeeal Plant-foods. 



The silt sample contained an abundance of magnesium-containing 

 minerals, and also of minerals containing iron, sodium, and calcium, 

 so that there is no danger of a deficiency of these essential elements 

 of plant growth should the land subsequently be brought into 

 cultivation. 



The above results furnish an example of the importance of a 

 mineralogical examination of a soil-type with a view to interpreting 

 the figures obtained by a chemical analysis carried out along con- 

 ventional lines. In the opinion of the writer too little attention is 

 paid to the possible aid which mineralogy may afford the soil-chemist 

 in his efforts to appreciate the special agricultural treatment 

 frequently needed by certain soil-types under an intensive system 

 of cultivation. 



In conclusion, the writer wishes to express his indebtedness to 

 E. H. Rastall, M.A., for his invaluable assistance and sympathy 

 during the progress of the work outlined above. Also to E. J. Roberts, 

 of the Cambridge School of Agriculture, for permission to use the 

 results of the analysis of the sample chosen for examination. 



SUMMARY. 



1. A sample of modern Fenland silt containing 8'98 per cent of 

 carbonate was found on mineralogical examination to include 

 dolomite as well as aragonite in its mineral assemblage. 



2. The dolomite is present in fresh angular crystal grains which 

 suggest a secondary and recent origin of the mineral. It has possibly 

 been deposited from sea-water which periodically covers the fore- 

 shore of the Fenland border of the Wash. 



3. The general mineral composition of the silt resembles closely 

 that of certain geologically recent deposits of Cambridgeshire, and 

 points to the boulder-clay left by the North Sea glacier as the chief 

 source of the material of which the silt is composed. The silt has 

 mainly been deposited by sea-currents which carry southwards the 

 eroded glacial deposits of the South Yorkshire and North Lincoln- 

 shire coasts. 



