ioo NOTES ON DOCKS AND DOCK CONSTRUCTION. 



Somerset Dock, at Malta, an expedient, resorted to with the 

 view of stopping the flow of water from a fissure which gave 

 a great deal of trouble, is described by Mr. 0. Andrews, M.I.C.E., 

 in his paper on that work, and of which description the following 

 is an abridgment : " The removal of the rock round the main 

 fissure, which had been left at 34 feet below the sea level, until 

 the invert (of the entrance) had been set, being proceeded with, 

 the discharge under so great a head increased daily, wedges 

 were driven in, but new openings were formed which increased 

 the evil. The pumping power available was collectively 143 

 horse-power, and the discharge from the fissures amounted to 

 7500 gallons per minute, but the labour of keeping so large a 

 number of engines and pumps in repair, under incessant work, 

 became so great that the water could not be kept down for any 

 practical purpose lower than 32 feet below the level of the sea. 

 To have obtained additional engine and pumping power from 

 England would have required some months, during which a 

 great outlay would have been incurred, or the works must 

 have been wholly suspended at a critical point. These con- 

 siderations led to an effort being made to check the flow in the 

 following manner. The water was allowed to rise to 28 feet 

 below sea level in order to relieve the pressure. A stage was 

 then erected, from which a guide-box was lowered over the 



Water Level in Dock 

 28 feet below Sea Level 



Surface of Rock 39 feet below Sea Level 



Pit cut in Rock to 43-9 

 below Sea Level 



FIG. 61. 



fissure ; within this guide-box a chisel 21 feet long was worked 

 by a ringing engine, by which means a pit was cut in the rock 

 to the level of 43 feet 9 inches below the sea (Figs. 61, G2). The 

 bottom of the hole was then roughly levelled and squared by 

 a diver. A block of limestone 6 feet 6 inches by 3 feet 6 inc 

 by 1 foot 5 inches having been prepared, a thick cushion or 

 bed of Pozzuolana mortar, protected by canvas, was secured to 



