GYPSUM. 114 
found to be iron sulpbate, and the acid globules to contain free sul- 
phuric acid. Hence the pyrites, under the influence of air and’ 
moisture, is oxidised to iron sulphate and free sulphuric acid. 
Oxidation of pyrites to iron sulphate and sulphuric acid is not 
usually very rapid, but I believe it is accepted that most, if not all, 
of the ‘‘ gob” fires in coal mines are traceable to the rapid oxidation 
of pyrites dust, in presence of moisture and coal dust. 
We have, then, in close proximity to the limestone, a material 
coal, whence iron sulphate and sulphuric acid are naturally produced. 
Further, I have broadly sketched to you whence and bow boulders 
of limestone could have been brought to the present position of the 
massive Gypsum nodules. We have only to imagine water impreg- 
nated with the oxidation products of the pyrites, flowing gradually 
into the waters in which the Red Marl and Rhetic beds were being 
deposited, to form an idea of the formation of massive Gypsum, and 
of all the crystalline and crystallized forms derived therefrom. The 
sulphuric acid of the Gypsum is one of the products of the pyrites 
derived from the denudation of the coal; another is red oxide of iron 
the red material which gives the colour to which the term ‘‘ Red Marl ” 
isdue. The red oxide of iron is produced by the action of the iron 
sulphate and sulphuric acid upon the limestone boulders. 
Calcium carbonate and iron sulphate react to form calcium sul- 
plate—Gypsum and iron carbonate. The sulphuric acid and calcium 
carbonate react to form Gypsum and free carbonic acid. The perco- 
lating water dissolves the carbonic acid and at the same time the iron 
carbonate, and carries it down into the clays, where under the influ- 
ence of atmospheric oxygen it undergoes further oxidation with the 
ultimate formation of that red oxide of iron, from which the red 
marl, as I have previously stated, draws its title. 
As you know no theory of this kind is worth much unless you 
can add something by experiment, outside the general speculation, to 
show that the theory is probable. In cases of this kind it is imposs- 
ible to perform an experiment on a large scale, as neither the vast 
