76 



THE MADRAS HARBOUR. 



required to keep this deposit of stone within bounds. If 

 the steamer drifts 50 feet while the doors are being opened, 

 130 tons of stone worth 260 rupees are wasted ; and if 

 dropped on the top of the bank already complete, but quite 

 out of sight, not only is the stone wasted, but it has to be 

 removed by divers at an expense far exceeding its original 

 cost. This department of the work is now nearly finished, 

 and I think with as few mistakes in the place of deposit as 

 has ever been accomplished in work of this kind. 



At the best, however, the top of such a bank of stone must 

 be rather irregular, and before the blocks can be set upon it, 

 it must be levelled. This is the work of the divers, who 

 descend from a boat moored just in front of the block work, 

 where by means of the overhanging Titan which I shall 

 presently describe, depths can be measured more accurately 

 than can be done from the surface of the ever-changing sea. 

 They make a perfectly level bed about 21 feet under water 

 on which the blocks can be set in true position. They after- 

 wards settle down two or three feet deeper by the consolida- 

 tion of the rubble below. 



The rubble base being now prepared to receive the concrete 

 blocks, we have next to see how the latter are prepared. The 

 use of concrete blocks in sea work is not of very old standing. 

 I believe I made the first myself about thirty years ago. 

 These were rather under 7 tons weight, and, being then con- 

 sidered too heavy, the weight was reduced. The blocks of the 

 Madras Harbour "Works are 27 tons. About one-tenth part 

 by measure consists of Portland cement, of which 23,323 

 tons have been imported from England and 4,440 tons 

 manufactured at Madras. The other nine-tenths consist of 

 broken stone and sand. The stone (granite from Palla- 

 veram) is crushed by machinery into pieces averaging the 

 size of an egg. Then this is lifted to the top of a platform 

 by machinery worked by the same engine that works the stone 



