64 



THE MADRAS HARBOUR. 



divers at all, it is as easy for them to work in 24 feet depth 

 as in 12 ; so why not make assurance doubly sure by going 

 to a depth about which there can be no doubt ? So in the 

 case of the Madras piers, and one or two other works 

 designed about the same time, the principle of founding in 

 the least depth possible was abandoned, and a depth adopted 

 which gave the most economical proportions of rubble stone 

 and concrete block work. But though 24 feet is more than 

 enough depth for the stability of rubble stone, it is not 

 enough for the stability of sand ; so if we had founded 

 directly on the sand we must have gone lower still, and 

 against this there were economical reasons which I need not 

 name here. 



Now that I have given my reasons for adopting an 

 upright wall, founded on rubble stone at a depth of 24 feet 

 below the surface, it may appear that, good as those reasons 

 may be for those parts where there is a depth greater than 

 24 feet, they do not suggest how the problem is to be solved 

 when the natural depth is less than 24 feet. If sand is an 

 unsafe foundation at 24 feet, what is to be done where the 

 sand is naturally only 12 feet under water ? And if rubble 

 stone is unsafe at 12 feet, what is to be done where there is 

 a natural depth of only 5 feet ? 



In this question is involved the history of the whole 

 difficulties of execution of the Madras Harbour "Works. 

 Where we have depth for our normal section its construction 

 Is all plain sailing. It is simply the application of the 

 calculated quantum of material, of machine work, of hand 

 labour. We laugh at Neptune. He cannot touch our sandy 

 bottom, because it is far below his limit of 24 feet. He 

 cannot touch our rubble stone, because it is far below his 

 limit of 12 feet, and hitherto he has not been able to disturb 

 our blocks at the surface because they are too heavy for any 

 force he has as yet been able to bring against them. 



