EFFECTS OF MINING. 605 



extent to deserve notice in a geographical point of view.* It ia 

 said, however, that in many places in the mining regions of Eng- 

 land alarming indications of a tendency to a wide dislocation of 

 the superficial strata have manifested themselves. Indeed, when 

 we consider the measm-e of the underground cavities which miners 

 have excavated, we can not but be surprised that grave catastro- 

 phes have not often resulted from the removal of the foundations 

 on which the crust of our earth is laid.f The 100,000,000 tons 

 of coal yearly extracted from British mines require the withdi-awal 

 of subterranean strata equal to an area of 20,000 acres one yard 

 deep, or 2,000 acres ten yards deep4 These excavations have 

 gone on for several years at this rate, and in smaller propo?-tion8 

 for centuries. Hence, it can not be doubted that by these and 

 other like operations the earth has been undermined and honey- 

 combed in many countries to an extent that may well excite seri- 

 ous apprehensions as to the stability of the surf ace.§ In any event 



* In March, 1873, the unprudent extension of the excavations in a slate mine 

 near Morzine, in Savoy, occasioned the fall of a mass of rock measuring more 

 than 700,000 yards in cubical contents. A forest of firs was destroyed, and a 

 hamlet of twelve houses crushed and buried by the slide. 



t The public journals in mining districts on both sides the Atlantic have, 

 within the last few years, contained frequent notices of extensive subsidences 

 in consequence of the removal of acres of coal from underlying veins. Several 

 casi3s are recorded as having occurred in Pennsylvania and in Belgium, in 

 which latter locality injurious effects have been augmented by injudiciously 

 depositing above the cavities huge heaps of stones and other waste from the 

 mines. Mineral springs, too, bring to the surface vast quantities of common 

 and other salts dissolved by the subterraneous flovring of the waters ; and, of 

 course, thus produce cavities in the earth. Tschihacheff describes a saline 

 spring in Asia Minor, which throws out a current of brine a foot in cross sec- 

 tion, no attempt being made to utilize the salt. Several English towns in the 

 neighborhood of salt mines seem exposed to danger of serious injury from the 

 removal of subterraneous strata by running water. Many persons have sup- 

 posed that the earthquake in Ischia, in 1881, which destroyed Casa Mieciola, 

 was occasioned by the action of mineral springs in washing out the deposits 

 on which the superficial strata rested. 



t See page 392, ante. 



§ It is now thought highly probable that extensive coal beds imderlie the city 

 of London at accessible depths, and it is proposed to attempt to raise from 

 those beds the supply for the British Capital, but the risk of undermining a 

 town with such a vast population will probably be considered too great to be 

 incurred at present. 



