128 TUNNELS. 



The cost of shafts varies in proportion to their depth, &c., &c. 



The cost of those in the Black Rock tunnel, Pennsylvania, in hard slate, was $79 50 per yard 

 down, or $18 72 per cubic yard. The shafts were seven feet in diameter, and 139 feet deep. 

 The cost per cubic yard of excavating tunnels has been in the 



Black Rock, hard grey wacke shite, (U. S.) $6.60 



Lehigh, very hard granite, (CJ. S.) $4.36 



Schuylkill, slate, (U. S.) $2.00 



Union, slate, (U. S.) $2.085 



Ellsworth, blue clay, lined, (Eng.) $1.545 



Box, freestone, marble, clay, &c., lined, (Eng ) $3.464 



Blaisy, exclusive of shafts, but including the lining, (France) $3.176 



Blue Ridge, cost per cubic yard $4.000 



The Blaisy tunnel cost, exclusive of shafts, $108 31 per lineal foot. 



In comparing the cost of tunnels in different countries, the difference of the price of labor should 

 be considered. This has not been done in any of the examples here given; the actual cost in 

 pounds sterling, &c., being simply reduced to dollars. 



The time required to drive the heading of the Black Rock tunnel was 1,243 days and 1,144 

 nights, or 2,387 spaces of 12 hours each, for 1,782.5 feet in length of tunnel. 

 For details of this tunnel, see the following tables. 



In the Kilsby tunnel, a working shaft 329 feet deep, much troubled with water, was finished 

 in seven or eight weeks. 



In hard rock, where continual blasting is required, two expert miners can run a &quot; branch&quot; 40 

 inches by 32 inches to the length of 10.5 inches in 12 hours. 



A tunnel cannot be pushed further than 500 feet without resorting to artificial means of venti 

 lation. 



Ventilation is found to be better in cold weather than in warm. 

 Headings are about 12 feet high ; width at base, that of tunnel at that height. 

 In the table on the succeeding p?ige, 

 P. L. means partly lined with masonry. 

 L. &quot; lined with masonry. 

 N. L. &quot; not lined with masonry. 

 Z. &quot; not stated. 

 S. &quot; has shafts. 

 S. S. &quot; supposed to have shafts. 

 C. &quot; average depth. 

 a. average per running foot taken from total cost. 



was constructed to drain the lakes in the valley of Mexico, to prevent overflows. 

 Measures are in feet and decimals ; 

 Time, in working days ; 

 Cost, in dollars and decimals. 



(X.) For details of construction of Kilsby tunnel, see American Railroad Journal, vol. I, new 

 series, (1838,) page 229 et seq. 



