MAN AND NATURE. 285 



they have been carried to greater depths than hereto- 

 fore ; following now in many places the beds of coal 

 as they dip under the magnesian limestone, and in 

 some instances rivalling the Cornish mines in their 

 extension under the sea. 



The working of the English coal mines is wonder- 

 fid, not only in the depths reached, but in the vast 

 extent of many of them, and the admirable pro- 

 visions made for their ventilation. In some of the 

 Northumberland collieries these being earliest in date, 

 as well as most extensive -the ventilating blast of air 

 forced down one shaft is made to circulate through 

 thirty or forty miles of subterranean workings before 

 emerging again at another. Well might we wish that 

 a better security could thus, or otherwise, be given 

 against those explosions of fire-damp which every 

 year, from casualty or carelessness, offer such fearful 

 records of calamity ! 



The deepest coal mine worked in Great Britain is 

 that of Duckinfield, in Cheshire, reaching 2,050 feet, or 

 more than a third of a mile, in its perpendicular depth. 1 

 But possibly the nearest approach to the centre of the 

 earth if we may thus speak of a fractional part 

 hardly exceeding y^-J-o^ of the actual distance is 

 that of a coal mine close to the sea at Wearmouth, 

 descending, we believe, about 1,800 feet below the 

 sea-level. This depth is recorded not only by the 

 great barometric pressure, but by the increasing tem- 



1 This extraordinary shaft, 12^ feet in diameter, was completed in 

 1858, after a labour of ten years. It reaches a bed of excellent coal, 

 nearly five feet in thickness. 



