" It naturally occurred to Mr. Mitchell, that the same means of resistance to downward pressure might be used, and he proposed to apply it for the foundations of light houses, beacons, and other structures, which for maritime purposes it might be desirable to place upon sand and mud banks, where hitherto it had been considered impracticable to place any permanent edifices. In the year 1S38, a plan for a structure of this nature for a lighthouse on the Maplin Sand, at the mouth of the Thames, was laid before the cor poration of the Trinity House, supported by the opinion of Mr. James Walker, their engineer. The 9 iron piles, 5 inches in diameter, with screws 4 feet in diameter, were accordingly driven 22 feet deep into the mud, and, with proper precaution, they were allowed to stand for two years, before any edifice was placed upon them. The lighthouse was subsequently constructed, and, as was testified by Mr. Walker, had stood perfectly until the present time (March, 1848"). The plan of the piling in this instance was octagonal, one pile being driven in each of the angles of the octagon, and another in the centre, making in all 9 piles, which were fixed in their places in 9 consecutive days, being screwed to a depth of 22 feet in the bank. The piles were made
of malleable iron, 5 inches in diameter, and 26 feet lung, with a cast-iron screw, 4 feet in diameter, screwed to the foot.
"Another lighthouse was erected to point out the entrance to the harbour of Fleetwood on Wyre; and under the advice of Captain Denham, 1: N., the screw-piles were adopted. The spot fixed on was the point of a bank of loose sand about two miles from the shore. Screw-iron piles, with screws of 3 feet in diameter, were forced about 16 feet into the bank, and upon them timber-suppo•ts, 48 feet in vertical height, were fixed, to carry the house and lantern. This structure was completed in six months, and it was said had never required any repairs to the present time," (March, 1815.) Another method of piling was invented by Dr. Potts, i but as this is connected more especially with PILE DRIVING, It has been described under that article, and does not demand any further observation in this place.