648 GEOLOGY OF OHIO. 
source of lithia at present is one of the minerals of the mica group, viz., 
lepidolite. , 
Titanic acid (Ti O,) has long been known as a constituent of some 
clays, but the report of New Jersey was the first to bring its unfailing 
presence to light in the clays of those districts. Reports of its dis- 
_ covery have from time to time, for thirty or forty years past, been circu- 
lated, but it failed to excite much attention. But its presence in small 
but persistent amounts is a constant factor in the later analysis. The 
source is believed to be menaccanite or titanate of iron, and experiments 
made by Cook strengthen that view. The amount varies from one or two- 
tenths per cent. to two per cent.; it is believed to be as neutral as so 
much sand would be in its effect on the clay. If this element is not re- 
ported in analysis it makes an error in both alumina and silica, as it 
fails to go to either perfectly. 
Sulphide of iron is an occasional constituent of clay, but has not 
yet been noticed in Ohio. ‘The other source of color noticed in clays is 
organic matter. The shades produced are all of a bluish-gray running 
to black and disappearing when the clay is burnt. The purer flint clays, 
like those of Portsmouth and Mineral Point, show a peculiar striping 
and veining which looks like concentric circles of vegetable growth. 
The color of the clay is light gray, and the veins dark blue, yet all turns 
to the same buff tint after calcination. In New Jersey, vegetable matter 
is frequently present in lignitic masses, but none of this is seen in Ohio. 
Organic matter does no harm unless the porosity produced by its ex- 
pulsion is a disadvantage, but saw-dust is often added to clays in which 
porosity is a desired element. 
Rare minerals containing such metals as cobalt, copper, zinc, and such 
salts as phosphate of iron are met in clays, but are exceptions and are of 
no importance in practical work. ‘Thus it appears that mineralogically, 
clays are kaolinite, mixed with sand, colored by iron and organic matter, 
and showing varying amounts of feldspar, mica, and other silicates and 
titanates. The chemical investigation of a clay should endeavor to 
present these facts, besides grouping those bodies together which are 
similar in action and effect. 
The following analyses, part of which were made in the Laboratory 
of the State University for the Geological Survey, and part from various 
sources, will indicate, it is hoped, those points which have been empha- 
sized in the foregoing discussion. They are, as will be seen, on the 
