" BLOWERS IN COAL-MINES. 141 



which has been already described as taking 

 place in wood coal, results in the formation of 

 common bituminous coal. As this process 

 continues, carburetted hydrogen and other in- 

 flammable gases are constantly evolved, and if 

 able to reach the surface, appear in the jets 

 just mentioned. If not able thus to discharge 

 itself, the gas remains pent up in the coal mines 

 until some unfortunate blow of the miner's 

 pick-axe strikes the place, and the gas issues 

 forth with great violence, and in alarming 

 quantities. Such a stream of gas is called a 

 " blower " by the miners. While, however, it 

 remains extremely probable that in every in- 

 stance bituminous matters form the source of 

 this gas, it is not so clear by what series of links 

 the necessary decompositions are effected. 



In addition to the evidences afforded us by 

 these gases of the really active operation of 

 deep-seated chemical forces, we may enumerate 

 sulphuretted hydrogen, sulphurous and hydro- 

 chloric acid fumes, sulphur itself, and ammonia, 

 as occasionally emitted from the earth's crust in 

 different countries, and under differing condi- 

 tions. The causes leading to their extrication 

 it is not possible to ascertain with certainty. 



The highly remarkable phenomenon of mud 

 volcanos ; that is, volcanos which instead of 

 lava, pour down enormous streams of mud, 



