233 



SEVERN TUNNEL. 



The Severn Tunnel is the largest work of the kind ever car- 

 ried out in England. It passes under the river about half a 

 mile below the railway ferry, and is 7,9 42 yards long, of which 

 3,960, or two and a-quarter miles, are under the bed of the river. 

 The depth of water over the line of tunnel at high water is 96 

 feet, and at low water 60 feet. It is lined with brickwork in 

 cement, the brickwork varying from 1 foot 10| inches to 3 feet 

 in thickness. The total cost is estimated at £1,500,000. 



CASCADE TUNNEL. 



The Cascade Tunnel on the Northern Pacific Eailway has 

 been commenced, and will be 9,880 feet long. 



Tunnels have been projected under Mont Blanc and the 

 Simplon, each being about twelve miles in length, but it is 

 feared that after the experience of the St. Gothard Tunnel the 

 heat in the centre of the tunnel would make it impossible for 

 human beings to live in the atmosphere. 



The great Dover Straits scheme has collapsed for a time, and 

 it is much to be regretted that a work which seems so prac- 

 ticable should be deferred. 



SUBMARINE BLASTING. 



Eegarding the removing of large masses of rock by tunnel- 

 ling and blasting, we have an excellent example in the recent 

 successful removal of Flood Eock in Hell Gate, New York Har- 

 bour, in October last year. By this one blast 200,000 cubic 

 yards of rock were so disrupted as to render its removal by 

 dredging an easy operation. The area of the work was nine 

 acres, and 225,000 pounds of giant gunpowder and 75,000 

 pounds of dynamite were used on this occasion. 



WATER SUPPLY. 



"Water supply is in this country at all events a very impor- 

 tant subject for discussion, and I do not propose to discuss this 

 question now, leaving it for those who have specially interested 

 themselves in the subject to deal with it at some future time, my 

 present intention being only to allude to the two great water 

 schemes now in progress, viz., those in Liverpool and New 

 York. 



YYENWY DAM. 



The Yyrnwy Dam, from which it is proposed to supply the 

 town of Liverpool, is to be built of masonry, and is to be 136 

 feet high in the centre, 1,258 feet long, and 117 feet thick in 

 its greatest width, impounding 1,118 acres of water, from 

 which an aqueduct 35 miles in length will convey the water to 

 the town. 



