THE FIRE-HARDENED ROCKS 



surface the temperature rose at a rate of about 1 of heat 

 (Fahrenheit) for every 125 feet. 



At the North Garden Gully Mine, Bendigo, Australia, 

 and at the New Chum Mine a temperature of 99 F. 

 was reached at 3000 feet, and 107 at 3645 feet. The 

 rate of increase of temperature was reckoned to be 1 of 

 heat (Fahrenheit) for every 80 feet. 



This rate of 1 for 80 feet was also found at a South 

 German mine, Maldon, as well as at a Ballarat mine, and 

 at a mine near Port Jackson. 



In a French mine more than 3000 feet deep, at the 

 collieries of Ronchamp, the rate of increase was as high as 

 1 in 50 feet. 



In the North Staffordshire mines Mr. Atkinson, 

 H.M. Inspector of Mines, found the increase to be on the 

 average 1 in 65 feet ; whereas in the South Staffordshire 

 Hamstead Colliery Mr. F. G. Meachem found that the 

 increase was 1 F. for every 110 feet. The same rate 

 was obtained at the Baggeridge Wood Colliery, South 

 Staffordshire. 



In South Wales, in the neighbourhood of Rhondda -and 

 Aberdare, the rate is 1 for 95 feet ; at Dowlais, in the 

 Merthyr coalfield, it was 1 in 93 feet; at the Niddrie 

 Collieries, near Edinburgh, the increase is at the rate of 

 1 J in 99 feet. 



It will thus be seen that all over the world there is an 

 increase of temperature at a rate which, on the average, 

 is about 1 for every 100 feet. There are 5280 feet in a 

 mile; therefore, if this rate of increasing temperature 

 were maintained, at a depth of 100 miles the temperature 



83 



