TRANSACTIONS OF THE SECTIONS. : 65 
would follow that sufficient time elapsed between the deposit of two successive veins 
to allow the perfect crystallization and formation of the lower one. 
It also yielded information interesting with reference to the ascertaining of the 
manner of the formation of coal, as it would authorize an inference that the material 
of which in this instance the bituminous vein was formed, was originally too soft and 
_ yielding, notwithstanding its present hardness and density, to fracture the boulder 
during the period of pressure necessary for its formation ; and also, that any mixture of 
gases or other ingredients acting or escaping during the formation of the bituminous 
coal, do not appear to have in any way affected the cannel coal deposited within it. 
On the relutive Position of the various Qualities of Coal in the South Wales 
Coal-Measures. By Stariine Benson of Swansea. 
The varieties of coal found in the mineral basin of South Wales may be classified 
under three heads :— 
1. Bituminous; the small of which will coke, 
2. Free-burning; which burns with rapidity, emits a considerable volume of flame, 
_’ and is best adapted for steam purposes, but of which the small does not coke. 
8. Stone adh and culm, or anthracite. 
7 These three varieties are not suddenly altered as they approach each other; on the 
contrary, there is often a gradual change from bituminous to free-burning within the 
_ limits of the same colliery, whilst the free-burning coals would also appear to become 
- eulms, burning without flame, probably from the diminution of volatile matter, before 
- the quality of the true anthracitic coal and culm is attained. 
The annexed sketch of the coal-measures between Pontypool and Kidwelly will 
serve to illustrate the position of each variety of coal. 
With a few exceptions, arising from portions of seams of coal removed from their 
original relative positions by faults or anticlinals, a central line of quality may be 
assumed to extend from Merthyr to Pembrey mountain near Llanelly; the bitumi- 
nous veins of coal on the south gradually becoming less so until they are free-burning 
in the centre, whilst these again change into culms, burning without flame, until the 
true anthracitic coals and culms are found on the north crop. 
Exclusive of the Pembrokeshire portion of the coal-measures, which is anthracitic, 
the dre between Pontypool and Kidwelly, where both crops merge in the sea, may be 
estimated at fully 750 square miles, of which about j ths consist of stone-coal and 
_ culms, 43ths of coking, smelting and free-burning coals. 
~ It is often remarked that each vein on the south crop gradually loses its bituminous 
- quality as it dips to the north, but the more southern veins not so rapidly as those 
“above them: and it has been suggested, that a line or plane @ dipping to the south 
_ might be so placed as to intersect each vein at a point where its relative proportion of 
_ bituminous quality has disappeared. 
South. 
Bituminous. 
- North. 
Anthracite. 
Supposing anthracitic coal to be formed by the removal of certain volatile matter, 
iefly oxygen, from bituminous coal by means of heat, may nota line, b, drawn at right 
angles to this intersecting plane, point to the direction whence such heat was derived 
from beneath the carboniferous measures? The surface-map, which shows that the 
_ seams of coal east of Merthyr are not anthracitic, but retain more of the bituminous 
1848, F 
3 
a. 
