SELENITE. I47 



age, it at least adds to the interest of Mr. Kenwortby's- 



discoveries, and contributes to the probability of his conclusions 



being correct by bringing the site in point of time more into 



line with similar discoveries elsewhere in this country, which, as 



Dr. Munro has pointed out, are mostiy of later date than those 



of the Continent. Apart from this particular consideration,. 



regarding which so little fresh evidence has been adduced, the 



filling of the stream presents features sufficiently interesting to 



warrant their record. 



[The Club is indebted to Mr. Reader's kindness for the blocks illustrating 

 his paper. — Ed.] 



SELENITE. 



BY W. H. DALTON, F.G.S., F.C.S. 



IN his paper on Sulphate of Lime in Essex Soils and Sub- 

 soils, published in the Essex Naturalist [ante, pp. 62-4),. 

 Mr. Dymond advances a novel view to account for the crystals 

 of selenite in the London Clay, viz., that the sulphate of lime is 

 supplied by the surface soil. He furnishes statistics to show 

 that the rainfall of 13 years would, apart from impoverishment 

 by the removal of crops, wash out all the sulphate in the soil,, 

 and argues, incontestably, that continuous replacement must be 

 in process. But for this he suggests that the lime is supplied by 

 the farmer, the sulphuric acid by the rainfall. The alternative 

 source which he propounds for the acid, fermentative action in the 

 soil, is an alternative more apparent than real, in that fermenta- 

 tion, or any process, biological or chemical, can affect only the 

 matter coming within its sphere of action ; it may modify the 

 compounds present, but cannot create such as are absent, and I 

 may remark that one such process is to separate, not to unite, 

 sulphuric acid and lime. The source of the sulphur, then, is the 

 point at issue; geologists generally say it is iron-pyrites; Mr. 

 Dymond, rainwater. 



That the water in house-tanks contains sulphates is undeni- 

 able, but are not these derived wholly from the soot of coal- 

 smoke, the bulk of which is precipitated on the roofs collecting 

 the rainwater ? What amount of sulphates would be found in 

 rainwater collected at a distance from such sources 

 of sulphur as coal-fires, brick-kilns, and sea-spray. And 

 why are not the waters off the chalky boulder-clay 



