used for Agricultural Purposes. 
407 
The following analyses of selected specimens of black shale 
from the mine at Cwmgynen in North Wales are illustrations of 
the variable character of this phosphatic mineral : — 
Composition of Four Samples of Black Silurian Shale. 
No. 1. 
No. 2. 
No. 3. 
No. 4. 
Organic matter and loss) 
on heating ( chieiJy black \ 
carbon or graphite) . . ) 
♦Phosphoric acid 
Magnesia 
Alumina, fluorine . . 
Carbonic acid, and loss . . 
Iron .. .. 3'511 Iron \ 
Sulphur .. 4'02J pyrites/ 
Sulphuric acid 
Insoluble siliceous matter 
* Equal to tribasic phos-l 
pbate of lime .. .. j 
616 
25-35 
33-58 
-31 
1-0I\ 
1-06/ 
7-52 
-17 
24-84 
4-87 
24- 78 
35-98 
•13 
1-08 
•21 
25- 11 
6-25 
23-31 
28-19 
5-22 
/ -58 
\ 1-21 
12-01 
/I -301 o.^Q 
{l-49/ ^ 
-16 
20-28 
3-67 
26-88 
35-36 
-2G 
1-89 
5-38 
22-94 
100 00 
100-00 
100-00 
100-00 
55-62 
50-08 
51-02 
5S-G8 
The specimens No. 1 and No. 2, it will be seen, contained 
over 7 per cent, of iron pvrites ; No. 3, 2f per cent ; and No. 4, 
about 3| per cent. Three of the specimens contained but little 
carbonate of lime, and merely traces of magnesia, whilst that 
marked No. 3 contained a good deal of carbonate of lime and 
magnesia. 
I fear there are considerable difficulties in the way of working 
these North Wales mines in which Silurian phosphatic black 
shale occurs, so as to yield a phosphate of sufficient value to 
be a marketable commodity. In most places it is found to be 
practically impossible to separate effectually the richer from the 
worthless or quite inferior phosphatic shales and limestone ; and 
in consequence the average specimens of the Welsh or Silurian 
phosphate mines often turn out verv poor in phosphate of lime, 
and much impregnated with oxide of iron and alumina, carbonate 
of lime, and similar objectionable impurities, which lower the 
commercial value of the mineral. Silurian or Welsh phosphate, 
therefore, in many places cannot be worked with economical 
advantage. 
Two cargo-samples of Welsh or Silurian phosphate analysed 
by me yielded the following results : — 
