270 
THE GEOLOGIST. 
argillaceous character, and contain from 30 to 34 per cent, of iron, giving 
oS water to the amount of from 32 to 35 per cent, of their weight by 
torrefaction. 
But, by far the most importaat produce of the Forest are the Brown 
Haematite ores, or hydrated per-oxides, which occur in such vast quan- 
tities, in what are called the " Mine Measures," and which, as already 
described, occupy the upper beds of the carboniferous limestone and the 
lower beds of the millstone grit. The diagram, page 226, shows a 
section of the " Mine Measures," and the section, page 267, shows the 
complete sequence of the beds in connection with the overlying Coal 
Measures. 
The ores are usually classified into 1, " Brush ; " 2, " Smith Mine ; " 
and 3, "Clod." — 1. The Brush-ore is a haematite, containing as much as 80 
percent, of iron, when pure; is compact, of a submetallic lustre, botryoi- 
dal, kidney-shaped, formed of concentric coats, and having a fibrous or 
radiated structure. More often, however, it is stalactitical, and covered 
with brilliant black crystals of hydrous oxide of iron, which are often 
60 minute and so thickly aggregated as to confer a velvetty appearance of 
great beauty. The local term " Brush " is probably derived from this 
stalactitic form. 
2. The Smith-ore consists of finely powdered per-oxide of iron, 
which occurs so pure as to be raised almost entirely free from 
extraneous minerals ; it usually contains from 54 to 58 per cent of iron. 
3. The Clod is a marl highly charged with the per-oxide of iron, 
and with small fragments of compact haematite or "brush." It is found 
under particular circumstances, to which I shall presently allude, and 
is valuable to a certain extent as a " flux" from the contained alumnia. 
The following are some analyses made by me of (average) samples of 
Forest of Dean ores : — ■ 
No. 1. 
No. 2. 
No. 3. 
No. 4. 
Per-osido of Iron 
62 
70 
80 
86 
Carbonate of Lime 
10 
0 
3 
0 
Silica 
6 
12 
6 
10 
Alumina 
4 
0 
0 
0 
Carbonate of Magnesia 
2 
4 
0 
0 
Manganese 
2 
0 
1 
0 
Water and Loss 
14 
14 
10 
4 
100 
100* 
100 
loot 
From this mineralogical description of the ores, let us turn to the 
* From Sandstone Vein. f Black Brush Ore. 
