274 
ON THE JUNCTION OF THE PEKMIAN AND COAL MEASURES. 
AT CONISBOROUGH. 
BY ROWLAND GASCOIGNE, F.G.S. 
The Section to which this Paper refers has been fully described in 
the Geology of the Yorkshire Coal Fields, (Memoirs of the Geolo- 
gical Survey of England and Wales) p. 479. 
A description may also be referred to in " West Yorkshire," 
p. 1 83. 
ON A CHEMICAL METHOD OF DISTINGUISHING BLACK OBSIDIAN 
FROM BLACK BLAST FURNACE SLAG. 
BY W. H. WOOD, F.C.S. 
The Sileca was determined in a piece of obsidian furnished by 
Mr. A. Campbell, Curator of the Halifax Museum, and in a black 
slag- from the Low Moor Iron Works, with the following- result. 
OBSIDIAN. SLAG. 
Silica 71-242 39-326 per cent. 
The large difference in the amount of this constituent suffices 
to distinguish the two substances. 
A partial analysis of the slag gave the results in column I, 
for comparisons sake an analysis of a slag- by Erdmann, quoted in 
" Greg- and Lettsems Minerology," page 131, is given in column 
II. 
L 
II. 
Silica 
... , 71-242 
74-80 
Ferric Oxide and Alumina 
12 444 
14-43 
Lime .. 
4-388 
1-96 
Magnesia 
0-015 
0-90 
Potash 
4-160 
6-40 
Manganese ... ' 
Trace 
1 -31 witb Fe O. 
Soda, Water, &c 
... undetermined 
The specific quantities of the obsidian and the black slag 
analysed, were found to be — 
Obsidian 2-60 
Black Slag 3-07 
