880 
PROCEEDINGS, lf^59 — 1<S70. 
stand any sudden change of temperature wlien intensel)^ heated, as in 
the case of the withdrawal of crucibles and the cooling of furnaces. 
In order to ascertain the degree of fusibility of each kind of clay it 
was baked or burnt to the state of an ordinary firebrick, from which 
portions were chipped so as to present several sharp, angular edges. 
These were placed in crucibles lined with powdered charcoal, and 
afterwards heated in a wind furnace to the fullest possible extent. 
After cooling, the comparative value of each was estimated by the 
degree to which it had resisted fusion, as shown by the thin edges of 
the broken piece being rounded or rendered translucent. To denote 
the power of resisting sudden changes of temperature without crack- 
ing, a crucible was made of each kind of clay, and after carefully 
drawing, they were subjected, without previous annealing, to the 
heat of an intensely heated furnace, and when thoroughly heated to 
the temperature of the furnace suddenly withdrawn and exposed to a 
current of cold air. On comparing the results of these experiments, 
it appeared that those clays which contained the minimum amount 
of oxides of iron and the alkaline earths are the best adapted to resist 
fusion, and least liable to crack upon being exposed to any sudden 
change of temperature, and the clays most serviceable for these pur- 
poses are those which approach nearest to the typical composition of 
one equivalent of allumina coml)ined with two of silicic acid and two 
of water. 
^Ir. Samuel Baines read a paper on some differences in the 
deposition of coal. In a previous paper he had advanced the opinion 
that the Yorkshire Freestone is an estuarine deposit, and being con- 
tinuous with the coal series further research has confirmed the 
opinion that the Coal-field generally is one large estiuirine deposit. 
The formation of the coal he surmised to be due more to the annual 
fall of foliage than to the stems themselves. Tlie reed-like Calamite 
has evidently been a water plant from its being found in such abund- 
ance in the black shale rather than in the coal itself. The presence 
of remains of bivalve shells and fish in cannal coal clearly proved that 
it was formed under water, and ordinary coal was probably accumu- 
lated in low, marshy islands or deltas in the mouths or estuaries of 
largo rivers. That it was a very quiet deposit is shown by the 
absence of water-worn pebbles. 
