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tight black shale or blue bind, for the former would allow 
the free escape of gaseous matter, and the latter would 
prevent its escape. It is well known that the character of 
the roof has a deal to do with the quality of the coal 
under it. 
Ordinary Meeting, April 7th, 1874. 
E. W. Binney, F.B.S., F.G.S., Vice-President, in the Chair. 
Mr. J. Sidebotham and Mr. J. A. Bennion were appointed 
Auditors of the Treasurer s Accounts. 
The Chairman exhibited to the meeting some portion of 
the cast iron roof from the Salford Station of the Lancashire 
and Yorkshire Railway, which after having been up for a 
period of four years was so much corroded and damaged 
that it had to be taken down. He attributed the effects to 
sulphuric acid and soot arising from the combustion of the 
coal used in the locomotives passing under it, aided by the 
action of steam and vibration. He referred to a paper by 
himself communicated to the Society and published Yol. II. 
(2nd series) of its Memoirs, on the effects of old coal pit 
water on cast iron, where similar results had been produced 
by sulphuric acid, carbonaceous matter, and water; also 
to a case alluded to by one of the most distinguished mem- 
bers of the Society, the late Dr. W. Henry, F.R.S., of the 
rotting of cast iron by the escape of steam from the junction 
of a pipe embedded in charcoal. Of course the rate of decom- 
position much depended on the quality of the iron ; but as 
that metal was now so much employed in building and 
mining operations, he considered it desirable to bring before 
the public every instance that came to his knowledge where 
it had been damaged or decomposed. 
