1S4 The Projected Mersey Tunnel and Railway. [April, 



ordinary circumstances. I liave, however, taken 20s. per cubic 

 yard for the excavation in the heading, which I beheve to be far 

 more than it can cost. 



That a tunnel, or as it is called, a subway, can in the estima- 

 tion of those competent to form an opinion, be carried under the 

 river Thames at a very small cost, is, I think, proved by the fact 

 that Parliament, last session, passed an Act for the " Tower Sub- 

 way," proposed by Mr. P. W. Barlow, F.R.S., C.E., son of the 

 highly-talented Professor of mechanics of that name, the capital 

 for Avhich is but 12,000Z., with power to borrow 4000?. 



This work is now in course of construction, and is to consist of 

 an excavation through the London clay 440 yards in length, hned 

 with cast-iron cylinders f " thick, with strengthened flanges, whose 

 external diameter will be 7" IJ", or 7 feet inside. 



At each end there will be a vertical shaft between 50 and 60 

 feet deep, fitted with lifts for the purpose of raising or lowering 

 passengers from and to a saloon carriage, which will at very fre- 

 quent intervals pass through the heading for the conveyance of 

 passengers. 



From each end the subway will fall towards the centre of the 

 river at an inclination of about 1 in 40 to a level under the river, 

 where the rails will be at a depth of 61' 6" below Trinity high- 

 water mark. 



With regard to the above, it may no doubt be said that it is as 

 yet only a matter of estimate ; and though given by an Engineer of 

 standing and approved by Parliamentary committees — one of whose 

 special duties it is to investigate the estimates for the purpose of 

 testifying to their sufficiency, — yet the estimate might prove falla- 

 cious. I now, therefore, proceed to give the cost of an important 

 work at Chicago, completed some time since, and in many respects 

 analogous to the one of which I am treating, but beset with some 

 difficulty not to be encountered in passing under the Mersey, arising 

 in great measure from the more uncertain material through which 

 the heading had to be diiven ; that at Chicago being clay, and that 

 at Liverpool red sandstone — the one being driven for two miles, or 

 3520 yards, under Lake Michigan, the other only 1300 yards under 

 the river Mersey. 



The Chicago tunnel was made by Mr. Chesbrough, C.E., 

 Engineer to the municipality of Chicago, for the purpose of ob- 

 taining a more ample supply of pure water for the inhabitants of 

 that important city from a point beyond the reach of sewage con- 

 tamination ; hence its great length. 



This work, embracing as it does two miles of heading carried 

 through clay, lined with two rings of brickwork, including a sum 

 of |120,000 expended on the two shafts and the appliances con- 

 nected therewith, cost |380,000, or 76,000/. 



