76 ANNUAL OF SCIENTIFIC DISCOVERY. 



the Pacific up the Marmoni to this point. This survey in connec- 

 tion with Mr. Kelley's gives a line of spirit-levels from ocean to 

 ocean that, following the bed of streams which flow transversely 

 across the isthmus, present the lowest possible profile. The result 

 showed a mountain area of 10 miles that would require to be 

 tunnelled, an undertaking too costly to be profitable, if within 

 the limits of engineering, while the other portions of this route 

 present the most favorable aspects. 



The southern portion of the Isthmus still remains to be ex- 

 plored. The government propose to continue these surveys the 

 coming season, which will be carried up the valley of the Tuyra, 

 across the divide to the Cacarica Lake, not far from the mouths 

 of the Atrato. This region was visited by Hellert, an experienced 

 German traveller, in 1845, who reported the divide not over 200 

 feet, but this is very unreliable, as he was so unfortunate as to 

 lose his instruments before it was reached. The expedition re- 

 turned to New York in July, and though not successful in finding 

 a proper route, have reaped a full reward for their labors in the 

 clearing away of all doubt from 3 separate routes, and their elim- 

 ination in the future from the field of research. 



CENTRAL SHAFT HOOSAC TUNNEL. 



At last, after years of toil, and at a cost of close upon half a 

 million of dollars, the great central shaft of the Hoosac has 

 reached the grade of the tunnel ; 1,030 feet below the natural sur- 

 face. This shaft is elliptical, the transverse diameter being 27 feet 

 and the conjugate 15 feet, passing the entire depth through a 

 compact mica-slate formation intermixed at intervals with white 

 quartz. At the commencement of the present contract with the 

 Messrs. Shanly, there required to be done 447 feet. This has 

 been accomplished since June 1, 1869, say in 15 months; giving 

 a monthly average of 29.8 feet. The largest month's work was 

 38 feet. At intervals of about 18 feet are floors of heavy timbers, 

 supported by " hitches " cut in the rock, connected by ladders, in 

 case of accident to the hoisting apparatus, and forming supports 

 for the wooden " guides," in which the cross-head travels, under 

 which is suspended the boiler-plate iron bucket, of a capacity of 

 about 400 gallons. The work has been impeded slightly by 

 water, of which the shaft makes nearly 3 inches per hour. To 

 raise this water, an engine of 60 horse-power is constantly work- 

 ing, pumping all the water which collects as far down as 650 feet, 

 caught in tanks by sloping " drip roofs." Below this, the water 

 on the bottom has been hoisted in the iron bucket, a bucketful 

 being sent up by the miners whenever the quantity became incon- 

 venient. Now, the shaft being at grade, a " sump " will be sunk 

 and a water-bucket with bottom valve used, thus avoiding the 

 tedious task of bailing into the bucket by hand. 



Workmen are now employed trimming the sides of the shaft, 

 and preparing the " guides " for a wooden cage to be substituted 

 for the bucket so soon as the "headings," east and west, at the 



