IROX-OKES. 301 
In the area under consideration we find workable ores in the 
Lower Lias of Lincolnshire, and in the Middle Lias of Oxford- 
shire, Northamptonshire, Leicestershire and Lincolnshire. 
The ores are usually obtained by open works at spots where 
the beds come to the surface, but in some cases the beds are 
worked in tunnels beneath a covering of other strata. In most 
cases the ore obtained is that known as Brown Haematite 
(hydrated peroxide of iron), and it consists mainly of those 
portions of the rock that have become weathered along the out- 
crop. The lowest beds exposed, and those otherwise procured 
from a depth, are usually grey or bluish grey, and they exhibit 
kernels of grey or green ironstone. 
In the grey unweathered rock, the ore is mostly in the form of 
carbonate of iron, while the green portions are probably coloured 
by silicate of iron, for, as Mr. A. B. Dick informs me, there is not 
a sufficient amount of phosphoric acid to produce any effect on the 
tint. Speaking of the Cleveland ore, Mr. Dick says " The green 
colour of the ore seems to be due to a silicate containing peroxide 
and protoxide of iron, but this could not be exactly determined 
because it was not found possible to dissolve out the carbonates 
without acting at the same time upon the silicate of iron."* 
The peroxidation of the ores, as pointed out by Mr. J. D. 
Kendall, has caused a general diminution in the volume of the 
strata, to the extent of about 12 per cent This furnishes an 
explanation of the open joints and the increased porosity of the 
ore at the outcrop, at the same time the iron is as it were more 
concentrated, f Hence the weathered beds furnish the richer 
ironstone. 
The quality of the different layers of ironstone is exceedingly 
variable in all localities, some of the beds being much more 
calcareous than others, arid the proportion of carbonate of lime is 
as a rule greater in the strata, and they are much harder, the 
further they are followed from the outcrop. Thus where the 
beds outcrop along a steep escarpment the ore is not so rich, and 
the expense of working it would be greater, than in those areas 
where the beds occur over a wide belt at the surface. 
Particulars concerning the strata having been previously given, 
it will be necessary only to add a few notes on the characters and 
qualities of the beds of ironstone : further remarks on the structure 
and origin of the beds are deferred for publication in the volume 
dealing with Oolitic ironstones. 
The iron-ore of Frodingham, in Lincolnshire, was recognized 
in 1859, and soon afterwards it was worked. 
The bed occurs in the Lower Lias (zone of Ammonites semi- 
costatus). Its maximum thickness is stated to be 30 feet, and 
owing to its slight dip (towards the east), combined with the level 
nature of the ground, its outcrop occupies a wide stretch of 
country. The average workable thickness of iron-ore is about 
* Iron Ores of Great Britain, Part I. p. 96. 
t Trans. N. of Eng. Inst. of Mining Engineers, vol. xxxv. p. 147 : see also Iron 
Ores of Great Britain and Ireland, 1893. 
