62 



SULPHATE OF LIME IN ESSEX SOILS AND 

 SUBSOILS. 



By T. S. DYMOND, F.I.C. 



[Read January 28th, 1905] 



IN his last Presidential address to the Essex Field Club, Mr. 

 F. W. Rudler traced the existence of Selenite in certain clay 

 strata to the oxidation of Pyrites in the London-clay, and the 

 reaction of the resulting sulphuric acid with carbonate of lime r 

 by which sulphate of lime is formed. The sulphate of lime 

 crystallizes slowly from solution at the ordinary temperature in 

 the form of selenite. I wish to suggest in this note that there 

 is another possible source for the selenite, and at the same time 

 briefly to discuss the practical bearing of the question upon Essex 

 agriculture. 



The selenite crystals appear to be most abundantly found in 

 certain superficial clay strata overlying the London-clay. In 

 sinking shallow wells at Upminster and other places in South 

 Essex, deposits of clay loaded with selenite are sometimes met 

 with. 1 The crystals are found in star like masses, each ray of 

 which consists of characteristic twin crystals superimposed 

 on each other. In the same part of the County, a dry bank 

 under a thick hedge is often found to be encrusted with a white 

 efflorescence of sulphate of lime, pointing to its abundance in the 

 surface soil ; if a drying wind occurs after rain, the surface of an 

 arable field will appear white for the same reason, and the farmer 

 finds the soil " capped " and hard. The water obtained from 

 wells sunk into gravelly pockets of the London-clay is often 

 excessively hard, the hardness being partly due to sulphate of 

 lime. In one such water from Wickford I found the permanent 

 hardness was equal to 93 parts of sulphate of lime per 100,000, 

 and another from Ingrave to 1 12 parts. In such waters, however, 

 part of the hardness is invariably due to sulphate of magnesia. 



That such excessive quantities of sulphate of lime are not 

 found associated with the Boulder-clay is sufficiently explained 

 by its permeability to water. The rain water draining through 

 the Boulder-clay dissolves from the surface and carries with it 

 the sulphate of lime, and the water issuing from springs at the 

 outcrop of the underlying gravel, contains appreciable, but not 

 excessive, quantities of the salt. Through the London-clay 

 water cannot easily percolate, and percolation is rather upwards 



1 Similar deposits were struck in cutting the new Woodford and Ilford railway. 



