Rofe — On the late Colliery Explosions. 107 



well, loaded to a disagreeable extent with the offensive vapour from 

 the cesspool. On continuing my observations with a barometer I 

 found similar results to those at the "blowing well" at Whittingham, 



These results, however, are exactly what, on consideration, would 

 be expected. The air in the well, on any diminution of the atmos- 

 pheric pressure, would necessarily expand and pass from the well, 

 and on any increase of pressure the reverse must take place. 



Now if we apply this reasoning to a coal mine, which, for the pur- 

 pose of this argument, may be considered as merely an immense 

 subterranean excavation, connected with the external atmosphere 

 only by the up and down cast shafts, we should expect the air in the 

 mine to expand when the atmospheric pressure is diminished ; and 

 if that expansion were sudden and great it would probably supply 

 as much air as the upcast was passing, without drawing an equi- 

 valent quantity of fresh air through the downcast ; and at the same 

 time, by tlie diminution of the pressure, the gas generated or con- 

 fined in the pores and fissures of the coal would be expanded or set 

 free more rapidly, and thus cause an excess of gas in the air of the 

 mine, which, if it meets with an open lamp, a smoker's pipe, or any 

 other means of ignition, spreads death and destruction around. 



It may, perhaps, be remarked, that if sudden variations of atmos- 

 pheric pressure acted in this way there would be more explosions 

 than there are ; but, fortunately, these dreadful accidents require a 

 concurrence of circumstances to cause them. There must be an excess 

 of gas in the mine, and, at the same time, whether from accident or 

 carelessness, a means of ignition. The chances are that these would 

 be only occasionally concurrent, and then, only, explosions would 

 take place. 



The lesson to be drawn from these remarks is that coal proprie- 

 tors should take especial notice of any considerable fall in the baro- 

 meter, and at such times force an extra ventilation either by additional 

 firing at the upcast, by a steam jet, or by any other means which 

 their experience may suggest; but by some means or other they 

 should increase the ventilation when any sudden diminution of 

 atmospheric pressure takes place. 



If there should be nothing new in the above remarks, I make no 

 excuse for offering them, because the consequences of these explo- 

 sions are so awful that it becomes the duty of every one to suggest 

 any precautionary measures he may have reason to believe could, in 

 any degree, tend to prevent them, even at the risk of exposing his 

 ignorance of what may have been already carried into practice. 



IV. — On some Fossils from the Lower Silurian Kocks of the 



South of Scotland. 



By Henry Alleyne Nicholson, B.Sc. 



(PLATE VII.) 



THE Lower Silurian Eocks of the South of Scotland, below the 

 level of the Wrae Limestone of Peeblesshire, though of great 

 thickness, and little altered by igneous agency, have as yet yielded 



