526 INQUIRY INTO THE STRENGTH 
few extracts from Professor Johnson’s inquiries, 
in order to compare them with similar carbo- 
naceous deposits found in the Swansea basin, and 
other parts of South Wales. In the latter dis- - 
tricts, as at Aberavon, Hirwin, &c., the beds of 
anthracite alternate with the bituminous forma- 
tions, sometimes composing the uppermost strata, 
but in most cases underlaying the bituminous 
coal. In some positions they pass into very thin 
lamine, and in others, the layers are so intermixed 
as to form the coal en masse. They, however, 
vary in quality, according to the district where 
they are found. The lower veins of the Bute col- 
liery, at the Hirwin and Plymouth iron works, 
according to Mr. Mushet, are partly anthraciteous, 
containing a greater or lesser degree of anthra- 
cite matter, accompanied with certain proportions 
of bitumen or carburetted hydrogen. 
The coal at the Yniscedwyn and Ystalyfera 
-works, in the Swansea valley, is entirely anthracite, 
containing nearly the same proportions of carbon 
as are exhibited in Professor Johnson’s experi- 
ments on the American specimens. 
The purest Welsh anthracite coal, such as the 
Yniscedwyn, Ystalyfera, and the lower stratum 
of Neath Abbey, contains about 90 per cent of 
