WATER IN FOUNDATIONS. 85 



of 11 feet above the sill level, or 24 feet below coping, That the 

 boils had their source in the sand bed, resting on the chalk 

 seemed proved beyond doubt, as the chalk wolds extended over 

 a large area, attaining an elevation of 500 feet, at no great 

 distance from Hull, and giving rise to copious springs at their 

 base. These boils were possibly as much due to land water 

 accumulated in the chalk as to any connection with the sand 

 beds of the Humber. That some such connection, however, did 

 exist is probable, as the water was brackish. A third boil soon 

 appeared, followed within a few days by the fourth, and in con- 

 sequence of the quantity of sand brought up, the ground began 

 to settle on the north and south sides and east end of the lock. 

 A crack appeared on the top of the river bank about 30 feet from, 

 and parallel to, the line of the river wharfing, and extended event- 

 ually 400 feet in length. That part of the bank between the 

 crack and the lock subsided vertically to the extent of 10 feet, 

 and in some places 12 feet. The settlement was gradual, and the 

 maximum was not reached until the foundation of the lock had 

 been made comparatively secure several months after the first 

 appearance of the crack. 



To strengthen the bank on the river side, clay was tipped 

 outside the river wharfing. Mounds of clay about 10 feet 

 high were also formed round the third and fourth boils, and 

 by this means the quantity of sand flowing from them was 

 much abated. The first boil was stopped, and was replaced 

 by a fifth which appeared on the westernmost cross row of 

 piling, and nearer than any other to the chain-pump, into which 

 it poured such a quantity of sand that a bank 6 feet high was 

 soon formed in the river near the place where the water was 

 discharged from the pump. This boil, which was one of the 

 worst, suddenly stopped, and reappeared 10 feet to the east of 

 the piling. In this position the boil continued to flow for four 

 months after its first appearance. 



In addition to the two rows of piles already driven across 

 the lock, two more were driven parallel to the centre line of 

 the lock, dividing the east end into six compartments. It was 

 determined to leave those in which the boils were until the 

 last. In the compartments free from them, the sand peat or 

 mud was removed over an area of about 4 yards square, divided 

 from the remaining area by sawn planks 5 or 6 inches wide, 

 and driven by hand. When a bottom of hard clay was found, 



