480 SECTIONAL TRANSACTIONS.—C, 
in the size and form in which it is found in the residues and in sections of 
silicotic lung tissue. Silica in the uncombined state (quartz) is also present 
in these residues as relatively coarse and fine grains ; it occurs, however, 
in amounts subordinate to sericite. Especially is this so with regard to the 
small number of quartz particles as compared with the countless fibres of 
sericite. One of the largest of these grains of quartz contributes as much 
silica, in a chemical analysis of a residue, as 1,630 fibres of sericite of the 
size found in the residue and in the lung tissue. 
Silica in the uncombined state is not the chief cause of silicosis. This 
appears to be established by : (a) the examination of the mineral residues 
and sections of silicotic lung tissue under the petrological microscope ; 
(6) the chemical analyses of these residues ; (c) the numerous cases of silicosis 
where rocks containing sericite are worked (e.g. South Wales Coalfield, the 
Rand, South Africa), and the complete absence of silicosis where silica rocks 
containing as much free silica (Scottish Coalfields) and even a higher per- 
centage (Kolar Coalfields, India) have been exploited by thousands of 
underground workmen for a long period of years ; (d) many cases of silicosis 
in mines where the ore and adjacent rocks contain only a low percentage 
of free silica ; and (e) by the fact that no silica rock hitherto investigated 
has given rise to silicosis-producing dust except those which contain sericite 
or fibrous minerals. 
It is submitted, therefore, that it is mainly the presence in the exploited 
rocks of fibrous minerals, be they sericite, sillimanite, tremolite, etc. (or 
a fibrous form of free silica as in chert, or a fibrous rock as in pumice), in 
aggregates which become freed into the atmosphere as individual fibres, 
that enables sufficient material in course of time to enter the lungs to cause 
silicosis. 
AFTERNOON. 
Excursion to the Carboniferous Limestone inliers of the Breedon 
district. Leader: Prof. H. H. SwINNERTON. 
Saturday, September 9. 
Excursion to the Pre-Cambrian and Cambrian of the Nuneaton district. 
Leaders: Prof. L. J. Wits, Dr. F. Raw, Mr. F. W. SHoTTON. 
Sunday, September 10. 
Excursion to the Pre-Cambrian of the Charnwood Forest area. 
Leaders: Prof. W. W. Warts, F.R.S., Mr. H. H. Grecory. 
Monday, September 11. 
Dr. A. Ratstrick.—The microspores of coal and their use in correlation (10.0). 
The microspore-content of coal samples can be extracted and isolated by 
the use of solvents such as Schultz solution, followed by ammonia, which 
remove the oxidisable coal matrix and leave the spore exines and micro- 
spores untouched. The microspores are mounted for micro-examination, 
and are dealt with statistically, in the same way as tree pollen in peat investi- 
gations. Microspore types are very varied and very definite, and their 
determination in the micro-separations is a matter of precision. There is 
