THE FIRE-HARDENED ROCKS 



no doubt the means he suggests would be effective, and it 

 would be possible, though with great difficulty, to keep 

 the workings cool.) 



When the borings extended to a depth of some miles it 

 would be necessary to freeze the bottom of the shaft. 

 This is a thing which is sometimes now done when a shaft 

 is being sunk through quicksands that may be encoun- 

 tered on its way down. Round the circle of the main 

 shaft a number of small bore-holes are driven, and into 

 them is poured very cold brine, which freezes the material 

 through which the shaft is to be driven. In the case of 

 the great boring we are considering this would have to be 

 done not only at the bottom of the shaft but also for 

 some time on the newly pierced shaft sides, until the 

 surrounding rock has been cooled for some distance from 

 the face. 



What would such a shaft cost ? How long would it 

 take to build ? What would the temperature be that it 

 encountered on the way down ? The following is the 

 estimate offered by Mr. Parsons : 



Cost Time in Temperature 



Years of Rock 



For 2 miles depth from the surface 500,000 10 122 F. 



4 1,100,000 25 152 



., 6 

 8 

 10 

 12 



1,800,000 40 182' 



2,700,000 55 212* 



3,700,000 70 242 



5,000,000 85 272 



But this estimate does not include the cost of cooling 

 the shaft or of providing it with air-locks. Mr. Parsons in 

 delineating the scheme remarked on the vast amount of 

 F 81 



