SELENITE.
147
age, it at least adds to the interest of Mr. Kenworthy'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 mostly 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