et 
TRANSACTIONS OF SECTION C. 1039 
In some of the sandstones which have been examined the barium sulphate is very 
unequally distributed, forming either a network or a series of small patches more 
or less spherical in shape. In such sandstone the sand grains which are uncemented 
by the sulphate are loose and readily separated from one another. Hence, when 
subjected to weathering, it presents a honeyecombed or mammillated appearance. 
In one bed which caps the Bramcote Hill, and which is usually described as the 
pebble bed, the removal of the intervening loose sand leaves little cemented masses 
about the size of a hazel-nut: these, however, are not pebbles in the ordinary sense 
of the word, but are merely sand grains cemented by the sulphate. 
I have attempted to trace some evidence of the way in which the barium ° 
sulphate has been introduced into the sand bed. It may have been deposited 
originaliy with the sand grains; but if this is its origin it has undergone physical 
change, since it now presents a compact crystallised mass. It seems certain, there- 
fore, that it has either heen originally deposited from solution, or has been rendered 
crystalline by the slow percolation of a solyent liquid through the sedimentary 
deposit. A third method seems possible. Bischof carried out experimentally the 
conversion of barium carbonate into sulphate by the action upon it of calcium 
sulphate solution; this double decomposition would produce barium sulphate 
together with calcium carbonate, and precisely such a mixture is found in the lower 
beds of the Hemlock Stone. 
As regards the possibility of barium sulphate existing in solution, as was supposed 
in an earlier part of this communication, I have yecently examined a stalactite 
which consists almost wholly of barium sulphate; and specimens of little sand 
masses hound together by barium sulphate in large crystals have also come into my 
hands. A solvent has in any case been present at some time, to cause the barium 
sulphate of these sandstones to assume the crystalline condition, since Bischof shows 
that the sulphate cannot be crystallised by fusion. 
13. Notes on Fuller’s Earth and its applications. By A. C. G. Campron. 
The author in this paper describes Fuller’s earth, its properties, and varieties. 
In its more concrete signification Fuller’s earth is the name applied to the red 
leamy stratum overlying the Inferior Oolite in the south of England. But its 
more general application is of economic and not of geological significance. He 
mentions that that dug from near the base of the Bedfordshire Greensand is of 
superior quality, and characterises it as a purifier of water. Fuller's earth in 
general is mentioned as a fine clay, less used now than formerly for cloth dressing. 
Considerable quantities are, however, still dug from the Lower Greensand and Oolites 
of the south of England for fulling and general cleansing purposes. Aspley Heath, 
on the brow of the Greensand escarpment, Woburn, Bedfordshire, is described as 
the locality where operations are presently gomg on for the purpose of procuring 
varieties of Fuller’s earth. Cylindrical holes, called ‘earth wells,’ are dug deep in 
the soft yellow sands, sometimes rocky with ferruginous lumps and thin carstone, 
in order to reach the Fuller's earth, which lies far down as a tabular and nearly 
horizontal mass, separated by not many feet of sand from the Oxford clay. Nearly 
two hundred years ago the pits were at Wavendon, an outlier of the Greensand, 
amongst the Oxford clay. A description of the beds is given as presently existing. 
Although superficially considered as all one earth, the substance is of three distinct 
kinds, which are mentioned, and their local names given. Allusions are made to 
substances dug in Warwickshire, the Isle of Skye, and Maxton Roxburghshire, as 
substitutes for Fuller’s earth, and a letter is quoted from a resident in Maxton 
bearing on this subject. The action of Fuller’s earth on peaty or otherwise dis- 
coloured water is described, with special allusion to, and description of, the 
‘Natural Mineral Water’ at Flitwick, Bedfordshire. Conflicting opinions as to 
this mineral water are given, with analysis supplied by Drs. Piesse and Johnstone, 
public analysts, London, and one published by a Professor White. Results of 
various experiments are stated, showing the efficacy of Bedfordshire Fuller’s earth 
as a filtering medium. The author is not prepared to say whether these filtra- 
