60 FOSSILIFEROUS H/EMATITE NODULES IN LEICESTERSHIRE 
show when this change probably did take place. The question 
is rather, how or in what manner did it take place ? Water 
no doubt played the chief part. This, supposing it were 
charged with carbonate of iron or possibly with perchloride 
of iron, would percolate the Permian strata by occupying 
any crevices, joints, or other openings, staining the rocks red 
by precipitating or depositing iron all around. As luematite 
is found pseudomorplious after ferrous carbonate, the 
latter, in the shape of the clay-ironstone nodules, &c., 
would naturally combine with ferric oxide. Now this kind 
of process, or segregation, seems to have continued until 
all the original carbonate of iron had become changed 
into haematite ; in fact, each individual nodule seems to 
have been a kind of centre of segregation, and taken up 
considerably more mineral matter than it originally con¬ 
tained, as evidenced by a comparison of their relative 
weights. The ferrous carbonates would, therefore, appear 
to have possessed, as it were, the power of attracting 
and absorbing or combining with the oxide of iron without 
increasing in bulk. But the most difficult point for explana¬ 
tion seems to be this :—What has become of the siliceous 
and aluminous materials of the original ore ? The foregoing 
analysis shows that they hardly exist in the pure ore ; and if, 
as I have supposed, the stones were once clay-ironstone, 
these earthy ingredients must have disappeared. The 
“ Spotted Vein ” clay-ironstone of Dowlais, Glamorganshire, 
is about the purest clay-ironstone I have heard of, if we may 
judge from the analysis given of it ;* and even supposing that 
the Permian nodules were originally composed of an ore as 
free from insoluble matter as this Glamorganshire ironstone 
is, there still remains the difficulty of solving the problem. 
Now, I understand that as yet chemists have not been able 
to account fully or satisfactorily for the way in which the 
removal of the silicates of alumina, &c., can be effected from 
a clay-ironstone. In a paper read before the Royal Geo¬ 
logical Society of Ireland, May 14tli, 1878, by Mr. E. T. 
* Silica and alumina. 14-17 
Peroxide of iron. 7661 
Red oxide of manganese . 1*21 
Lime. 3-13 
Magnesia . 3-96 
Phosphoric acid. 0 57 
Potash . 0-87 
Sulphur. 006 
100-58 
See “ Iron Ores of Great Britain,” Part iii., p. 209. 
