88 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



long driven at right angles to the line of the lock, and the 

 easternmost of these spaces was "again divided by a row of sawn 

 4-inch planks driven in the same direction. 



It was decided to substitute brickwork for concrete in this 

 compartment for the following reasons : When the bottom of 

 the foundation was of sand, boils had on more than one occasion 

 broken out soon after the concreting had been commenced ; and 

 it was believed that the fall of the concrete from the barrows 

 on the sandy bottom, which thereby assumed the nature of a 

 quicksand, accelerated their appearance. Moreover, by adopting 

 brickwork, as soon as the requisite depth had been reached over 

 a small part of the area to be excavated, this portion could at 

 once be made secure; whilst, on the other hand, the bottom 

 could not be made secure with concrete until an area of con- 

 siderable extent had been excavated to the required depth. 



In the two areas divided by the sawn planking the following 

 plan was adopted : As soon as a space about 3 yards square 

 had been reduced to the required depth, a flagstone about 5 feet 

 square was set in a bed of concrete made with Medina cement, 

 the upper surface of the flag being level with the bottom of the 

 foundation ; on the centre of this flag a small chain-pump was 

 fixed, and four courses of brickwork set in Portland cement were 

 laid over the bottom of the foundation as fast as it could be 

 excavated, the brickwork overlapping the flag and forming a 

 well-hole for the pump, from which also a channel about 1 foot 

 wide, with a bottom of flagstones, was left up the centre of the 

 foundation; so that in the event of a boil bursting out, the 

 foundation could be drained to the lowest level required, whilst 

 the pump-hole remained secure and available to the last. The 

 eastern half of the sixth compartment was thus covered with 

 four courses of brickwork; the pump was then removed, and 

 the foundation levelled with a layer of concrete 1 foot thick, 

 made with Portland cement. In the western division of this 

 same compartment, a boil which was still in an active state 

 was first surrounded on three sides with 4-inch planking, driven 

 by a small hand-engine. With the exception of the space, 33 

 feet by 7 feet, so enclosed, this division was dealt with in the 

 same manner as the last. 



To overcome the larger boils, some castings were made which 

 it was thought would be an improvement on the stones per- 

 forated, as described above. These castings were in the form 



