SECTIONAL TRANSACTIONS.—C. 479 
connect with the Midland Coalfields. In the Vale of Clwyd the limestone is 
overlaid by the Purple Sandstone, usually ascribed to the Lower Coal 
Measures. Coal Measures of limited extent are known under the Drift 
in Anglesey. 
Carboniferous rocks were probably never deposited on Snowdonia, the 
Denbighshire Moors and the Clwydian Hills. The western extension of 
St. George’s Land across the Channel to Ireland is questionable. 
Mr. T. Eastwoop. 
South Staffordshire furnishes examples of proximity to land during 
Upper Carboniferous times—the ‘ Silurian banks,’ extending as north-to- 
south peninsulas or islands to the north of St. George’s Land. ‘These 
banks were completely submerged before the Upper Coal Measures were 
deposited, though land still occurred to the south as is evidenced by the 
overstep of the Halesowen Group and by other facts. 
In Warwickshire there was land, probably an island, north of Nuneaton. 
South of Nuneaton basal Coal Measure Shales rest upon Cambrian Shales 
indicating deposition in quiet waters some distance from a shore-line. 
Later, at Dosthill, an island of Cambrian Shales contributed breccia to the 
Etruria Marls, while in the same locality the Productive Measures show 
few signs of proximity to land. "The Cambrian Shales also contributed 
material to the Etruria Marls at Nuneaton; but farther south the latter 
formation is barely distinguishable from Productive Measures, and this 
suggests a northerly provenance, though land probably lay some distance 
to the south and furnished material for the Corley conglomerates. 
Between the Warwickshire and Leicestershire Coalfields the Trias rests 
on older rocks probably folded along meridional axes of pre-Triassic date. 
In borings at Chilcote and Desford rocks were encountered which may be 
interpreted as shore-line deposits. 
Dr. W. R. Jones.—Silicosis : the minerals which cause it (12.15). 
The definition accepted at the International Congress on Silicosis at 
Johannesburg, in 1930, was, ‘ Silicosis is a pathological condition of the lung 
due to inhalation of silica dioxide,’ and that ‘ to produce the pathological 
condition, silica must reach the lungs in a chemically uncombined con- 
dition.’ Also, under English law (Silicosis Scheme for compensation), free 
silica is the basis: ‘ For the purposes of this Scheme (No. 342 of 1931) 
silica rock means quartz, quartzite, sandstone, gritstone or chert, but does 
not include natural sand or rotten rock.’ 
Cases in the anthracite district of South Wales came under the direct 
notice of the author, however, where no rock of the type named in the 
Scheme occurred in the underground working-places of the deceased, 
although post-mortem examination confirmed silicosis as the cause of death. 
It was therefore decided to investigate the possibility that rocks other than 
those included in the Scheme caused silicosis. This was done by examining 
the mineral residues from twenty-nine lungs, each from a person whose 
death had been certified as due to silicosis or to silico-tuberculosis. "The 
cases include potters, colliery workers, a stone-mason, and a silica-brick 
worker. Residues from other lungs have also been examined (fifty-one in 
all) ; they include pulmonary cases other than silicosis, and a normal lung 
used as control. 
The bulk of the mineral residues obtained from each of the silicotic lungs 
consists of minute fibres of sericite. ‘This mineral is abundantly present 
also in all the rocks which gave rise to the inhaled dust ; it is present in these 
